The Clay Minerals Society Glossary of Clay Science, 2019 version

Part 2. Natural Clay-Related Materials



achlusite a poorly defined material, possibly sodium mica



adamsite an obsolete term for muscovite



adularia see alkali feldspar



agalite an obsolete, local term for a fibrous talc from New York State, USA; or for pyrophyllite from China (also obsolete)



agalmatolite an obsolete term for pyrophyllite or a mixture with dominant pyrophyllite



albite see feldspar, alkali feldspars



aliettite a regularly ordered interstratification of a talc-like layer and trioctahedral smectite-like layer in a ratio of 1:1 (Veniale and van der Marel, 1969; Bailey, 1981). Cf., interstratification



alkali feldspar Alkali feldspars represent a subgroup of feldspar minerals occurring in the solid solution series between albite [Ab: Na(Si3Al)O8] and orthoclase [Or: K(Si3Al)O8] end members. The series includes minerals of albite, sanidine (a high-temperature monoclinic polymorph of K-rich feldspar with disordered Al-Si distributions, occurs in lava flows), microcline (triclinic polymorph of K-rich feldspar, may be referred to as low, intermediate and high for variations in temperature of occurrence, and "maximum" with ordered Al-Si distributions), adularia (a K-rich feldspar with monoclinic and triclinic domains formed from partial Al-Si order states, often designated as a varietal name, occurs hydrothermally, in pegmatites and under diagenetic conditions), and orthoclase (a K-rich feldspar with an intermediate Al-Si ordering state, occurs in small plutons at moderate depths). The boundary between albite and sanidine is at ~ Or40 (i.e., ~ 40 mole % of K-rich feldspar) and this region between Ab90 to ~Or40 (with <10 mole % of anorthite component) is also defined as "anorthoclase". Cf., feldspar

allevardite obsolete name replaced by rectorite, see rectorite



allophane a semiordered hydrous aluminosilicate, Al2O3(SiO2)1.3-2.02.5-3.0(H2O), that is closely related to imogolite because both seem to be incipient 1:1 minerals structurally and chemically, although it has been suggested that allophane may be an incipient montmorillonite. The ratio of SiO2 to Al2O3 is usually 1.3 to 2.0 for allophane, but has been reported as low as 0.83, a greater variation than in imogolite. Allophane shows curved walls with a more spherical morphology (30 - 50 spherical diameters) than imogolite, which is tube-like. Allophane is common in soils derived from volcanic ash, but may be present in soils derived from basic igneous rocks in tropical climates or in podzol soils derived from more acidic rocks. Allophane may precipitate in hot springs rich in silicic acid and aluminum. Allophane is white or colorless when moist, but earthy when dried. Syn., disordered allophane, Cf., imogolite

aluminoceladonite a dioctahedral member of the true mica group. The end-member formula is KAl(Mg,Fe3+) Si4O10(OH)2, where = vacancy. Typical range in composition is: viR2+/(viR2+ + viR3+) 0.25, viAl/(viAl + viFe3+) = 0.5 - 1.0, Mg/(Mg + viFe2+) > 0.5 (Rieder et al., 1998).



alurgite an obsolete varietal term for manganoan muscovite and manganoan illite



alushtite known only in the Russian literature and not an official mineral name; the accepted name is tosudite



amesite a (trioctahedral) platy serpentine mineral of ideal composition of Mg2Al(Si,Al)O5(OH)4. Fe2+, Mn, Cr, Ni, and vacancies may substitute for Mg and viAl in natural samples. Natural occurrences are rare and have been noted from the Saranovskoye chrome deposit, North Urals Mountains, Russia; Chester, Massachusetts, USA; Mount Sobotka, Poland; Postmasburg, South Africa; Lake Asbestos Mine, Black Lake, Quebec, Canada; and Antarctica. The Quebec occurrence involves a rodingitized granite within a serpentinized peridotite. Stacking disorder is common but, where regular layer stacking occurs, it is most often based on a distorted 2H2 layer sequence (space group C1). Cf., kellyite, zinalsite.



ammochrysos an obsolete term for muscovite



ammonium hydromica an obsolete term for tobelite



ammonium muscovite an obsolete term for tobelite



amphilogite an obsolete term for muscovite



anandite a trioctahedral member of the brittle mica group. The end-member formula is: BaFe2+3(Fe3+Si3)O10S,OH. Typical site substitutions include: Ba > K,Na; Mg, Fe3+, Mn, Al for Fe2+; and S > OH,Cl,F. Anandite occurs in a banded magnetite-barite-sulfide ore within meta-sedimentary granulite facies at the Wilagedera iron ore prospect, North Western Province, Sri Lanka, and it has been reported at Rush Creek and Big Creek, Fresno County, California, USA, and Sterling Hill, New Jersey, USA, although the latter occurrences are in doubt because of the lack of structural S, a requirement for the species (Bujnowski et al., 2009). Anandite occurs as 2O and 2M1 polytypes, and a 2M polytype based on a 1M stacking sub-structure.



anauxite a discredited term for kaolinite



andesine see plagioclase feldspar



ankangite a discredited manganese oxide mineral better described by the H2O-free variety of mannardite, see hollandite

annite a trioctahedral member of the true mica group. The ideal end-member formula is KFe2+3 AlSi3O10(OH)2. The ideal end-member composition is unlikely to occur because of tetrahedral-octahedral misfit (the inability of the tetrahedral sheet to link with the octahedral sheet at certain compositions), with at least 10 % Fe3+ required to minimize misfit. Annite occurs in granites, granitic pegmatites, greisens, and some alkalic (syenite) rocks. Annite forms most commonly in the 1M polytype and belongs to the collective name "dark" mica. Cf., biotite



anomite an obsolete term for biotite



anorthite see feldspar, plagioclase feldspar



anorthoclase see alkali feldspar



antigorite a platy serpentine with lath-like characteristics. Diffraction studies have shown an atomic superstructure arrangement approximately along the [100] direction. The origin of the superstructure is the tetrahedral repeat unit involving tetrahedral reversals in + or - directions along the c axis to form a wave-like structure. Antigorite structures have been shown by single-crystal X-ray diffraction to have, for example, a wave structure involving a tetrahedral repeat of 17 and one with two waves of tetrahedral repeats of 16, although other wavelengths are possible (from 12 to 21). For the 17 tetrahedral repeat, there is a half-wave width of 8 tetrahedra and 9 tetrahedra (Capitani and Mellini, 2004). At one reversal in each unit cell, there are 4- and 8-fold tetrahedral rings, but only 6-fold tetrahedral rings at the other reversal. Between reversal points, the tetrahedral rings are 6-fold. The generalized formula is ideally: M3m-3T2mO5m(OH)4m-6 where M = six-coordinated cations, T = Si, Al, and m = tetrahedral repeat along the superstructure direction, usually the [100]. M is predominantly Mg, but may have Fe (mostly Fe2+), Ni, Cr, and Al. Because each superstructure type affects the composition, these forms are not sensu stricto polymorphs of each other or between lizardite and chrysotile. Each half wave has a curvature, either concave up (+ c axis) or concave down (- c axis). The interlayer in an ideal serpentine is occupied by hydrogen bonds, which link adjacent 1:1 layers. In antigorite, linkage across this region is by tetrahedra, and polytypism cannot describe the stacking structure. For m = 17, the space group symmetry is Pm, for m = 16, the space group is C2/m. Antigorite is commonly found in igneous or metamorphic serpentinites. Serpentine rock is mostly comprised of antigorite and lizardite. Cf., carlosturanite, chrysotile, lizardite

antrophyllite a poorly defined material, possibly a mica



aphrosiderite an obsolete term for chlorite filling cavities in igneous rocks, possibly chamosite



armbrusterite a modulated 2:1 layer silicate with a continuous octahedral sheet containing Mn and Na and tetrahedral sheets having 5-, 6-, 7-, and 8-fold tetrahedral rings (Yakovenchuk et al., 2007). One symmetry-unique Si tetrahedron is inverted relative to the others in the sheet and this tetrahedron links two adjacent tetrahedral sheets. The other tetrahedra link to the octahedral sheets. The ideal chemical composition is K5Na6Mn3+Mn2+14(Si9O22)4(OH)10 . 4H2O. Armbrusterite is found in the Khibiny alkaline massif, Kola Peninsula, Russia. Cf., bementite, parsettensite, pyrosmalite, innsbruckite, varennesite



asbestos see Part 1 of Glossary



aspidolite a trioctahedral member of the true mica group. The end-member formula is NaMg3AlSi3O10(OH)2 and it occurs most commonly as the 1M polytype. Aspidolite is rare and can occur in meta-evaporates, in chromite sequences of mafic/ultramafic layered intrusions, gabbraic xenoliths, and metapelites. In older literature, aspidolite is referred to as sodium phlogopite (a term now considered obsolete).



astrolite an obsolete term for muscovite



astrophyllite see astrophyllite group



astrophyllite group The general formula (as given by Sokolova and Hawthorne, 2016) for the astrophyllite group minerals is A2pBrC7D2(T4O12)2IXOD2XOA4XPDnWA2 where C represents cations at the M(1-4) sites in the O sheet and are commonly Fe2+, Mn, Na, Mg, Zn, Fe3+, Ca, Zr, Li; D represents cations in the H sheet and are either in 6 or 5 coordination and are Ti, Nb, Zr, Sn4+, 5Fe3+, Mg, Al; T = Si, Al; A2pBrWA2 (I block) with p =1, 2; r = 1, 2; A = K, Rb, Cs, Ba, H2O, Li, Pb2+, Na, where = vacancy; B = Na, Ca, Ba, H2O, ; Xo refers to anions in the O sheet not bonded to T sites, XOD = oxygen anions in common at the 3M and D vertices; XOA = OH, F anions at the common vertices of 3M polyhedra; XPD = F, O, OH, H2O, , apical anions of D cations at the edges of the HOH block; WA = H2O, ; and for XPDn, n = 0. 1, 2.

The astrophyllite group minerals form 2:1 phyllosilicate-type structures with portions of the structure described as HOH (analogous to TOT in 2:1 phyllosilicates) with T4O12 ribbons comprising the H (heterogeneous, hetero- meaning "extra") sheet. Alternating with HOH blocks are intermediate (I) blocks along the c axis. Sokolova and Hawthorne (2016) described the astrophyllite group as a "supergroup" with three divisions (groups): the astrophyllite group, the kupletskite group and the devitoite group. HOH blocks may link directly (as in astrophyllite group, with Fe2+ dominant) or do not link (as in devitoite group) or direct linkage with Mn2+ dominant (as in kupletskite group). The linkages involve "bridges" of D-XpD-D. These titanosilicates have similar a axial lengths to phyllosilicates (both near 5.4 ) and d(001) values (~10.9 , although somewhat variable vs 10.0 in 2:1 phyllosilicates). The supergroup divisions are:



Astrophyllite Group, Fe2+ dominant, direct HOH linkage

astrophyllite K2NaFe2+7Ti2(Si4O12)2O2(OH)4F

iobophyllite K2NaFe2+7(Nb,Ti)(Si4O12)2O2(OH)4(F,O)

zircophyllite K2NaFe2+7Zr2(Si4O12)2O2(OH)4F

bulgakite Li2(Ca,Na)Fe2+7Ti2(Si4O12)2O2(OH)4(F,O)(H2O)2

nalivkinite Li2NaFe2+7Ti2(Si4O12)2O2(OH)4F(H2O)2

tarbagataite (K )CaFe2+7Ti2(Si4O12)2O2(OH)5



Kupletskite Group, Mn2+ dominant, direct HOH linkage

kupletskite-1A K2NaMn7Ti2(Si4O12)2O2(OH)4F

kupletskite-2M K2NaMn7Ti2(Si4O12)2O2(OH)4F

kupletskite-(Cs) Cs2NaMn7Ti2(Si4O12)2O2(OH)4F

niobokupletskite K2NaMn7(Nb,Ti)(Si4O12)2O2(OH)4(O,F)



Devitoite group

devitoite Ba6Fe2+7Fe3+2(Si4O12)2(PO4)2(CO3)O2(OH)4

sveinbergeite (H2O)2[Ca(H2O)](Fe2+6Fe3+)Ti2(Si4O12)2O2(OH)4(OH,H2O)

lobanovite K2Na(Fe2+4Mg2Na)Ti2(Si4O12)2O2(OH)4



HOH blocks are found in other (heterophyllosilicate) titanosilicates, and these minerals have been described by Ferraris and co-workers (e.g., for a partial summary, see Ferraris, 1997, Sokolova, 2006, Jin et al., 2018). These include:

nafertisite [Na,K, )4(Fe2+,Fe3+, )10(Ti2O3Si12O34)(O,OH)6],

bafertisite [(Ba2(Fe,Mn)4Ti2(Si2O7)2O2(OH)2F2,

jinshajiangite (Na,Ca)(Ba,K)Fe4Ti2(Si2O7)2O2(OH)2F,

perraultite (Na,Ca)(Ba,K)Mn4Ti2(Si2O7)2O2(OH)2F,

lamprophyllite Na2(Sr,Ti,Na,Fe)4(Ti2O2Si4O14)(O,F)2,

seidozerite Na1.6Ca0.275Mn0.425Ti0.575Zr0.925(Si2O7)OF,

and many others. The titanosilicates are found in hyperagpaitic (highly peralkaline nepheline syenites) rocks.



attapulgite 1) refers to the mineral, palygorskite, and should not be used in the mineralogic or geologic literature. See Guggenheim et al. (2006) and references therein. 2) Attapulgite is a common, globally used industrial term synonymous with palygorskite; especially, where mined and processed in the Florida-Georgia region of the United States or other commercial deposits around the world (e.g., China, Spain, Senegal, India, Australia, Greece, Turkey and Ukraine).



augite a common clinopyroxene with wide ranges of solid solutions, (Ca,Mg,Fe2+,Fe3+,Ti,Al)2(Si,Al)2O6. Si may be replaced by Al (~ 2 to 10 mole %). Ti-bearing augite may develop sector zoning (or hourglass zoning). Exsolution lamellae of Ca-poor pyroxene in augite crystals are common. Augite occurs in mafic or ultramafic igneous rocks and in high-grade metamorphic rocks. See pyroxene group for additional details.

avalite a poorly defined material, possibly chromian illite or a mineral mixture



baddeckite a poorly defined material, possibly muscovite and hematite



bafertisite see astrophyllite group



baileychlore the trioctahedral Zn-rich member of the chlorite group. Also, see Part 1. General terms: group names, chlorite



balestraite a member of the mica group characterized by octahedral vanadium and lithium and free from Al and OH, with a chemical composition of ideally KLi2VSi4O12. Balestraite occurs in subgroup C2 symmetry because of octahedral ordering and as a 1M polytype. Balestraite occurs in Mn-rich beds within metacherts of an ophiolite sequence and was located between carbonate-rich and hematite bands at the Cerchiara mine, Eastern Liguria, Italy.



baltimorite see picrolite



bannisterite a modulated, trioctahedral, mica-like layer silicate with cross-linked inverted tetrahedra with an idealized formula of Ca0.5K0.5M10(Si14.5Al1.5)O38(OH)8 . nH2O where M is medium-size divalent cations, such as Fe, Mn, Zn, Mg, and n = 2 - 6 (Heaney et al., 1992). The tetrahedral sheet consists of 5-, 6-, and 7-fold rings. Important localities for bannisterite include Franklin, New Jersey (USA), Broken Hill, Australia, and Nyberget, Sweden; localities with abundant Mn silicates.



barbertonite see hydrotalcite group



bardolite a poorly defined material, possibly interstratified biotite and vermiculite

basonite a poorly defined material, possibly interstratified biotite and vermiculite



bastite an obsolete term describing a pseudomorph comprised of serpentine altered from a Mg-rich pyroxene



barium phlogopite an obsolete varietal term for phlogopite



barytbiotite an obsolete varietal term for phlogopite



bastonite a poorly defined material, possibly interstratified biotite and vermiculite



baumite discredited name because it is a mixture of several phases; see caryopilite



bauxite see Part 1 of Glossary



bavalite an obsolete term for oolitic chlorite, possibly chamosite

bayerite a polymorph of Al(OH)3 that occurs rarely in nature. The gibbsite Al(OH)3 octahedral layer is similar to the dioctahedral layer in bayerite, but the stacking of the layers differs. Small distortions in the bayerite octahedra produce an overall two-layer structure. A notable occurrence for bayerite is in sedimentary rocks from Hartrurim, Israel, where bayerite is in association with calcite, gypsum, portlandite, and ettringite. Cf., gibbsite, nordstrandite



beidellite a dioctahedral member of the smectite group. An important characteristic of this member is that isomorphous substitution occurs primarily in the tetrahedral sites to produce the net negative charge on the 2:1 layer (Güven, 1988). An idealized formula for beidellite is R+0.33Al2(Si3.67Al0.33)O10(OH)2.nH2O, where R is an exchangeable cation, in this case univalent, but other valences are possible. The iron (Fe3+) analogue is known as nontronite and intermediate compositions are known. Beidellite is found abundantly as weathering products of volcanic ash, in association with hydrothermal environments, and as diagenetic products. An especially pure end-member beidellite comes from the Black Jack Mine, Idaho, USA. Cf., smectite.



bementite a modulated 1:1 layer silicate with octahedral sheets interlayered by a continuous tetrahedral sheet with double 6-fold tetrahedral rings (Heinrich et al., 1994). The 6-fold rings are interconnected and have tetrahedra pointing up and down, and adjacent octahedral sheets are connected with 5- and 7-fold tetrahedral rings. The ideal chemical composition is M7Si6O15(OH)8, where M are medium size cations, such as Mn, Fe, Mg, Zn. Small amounts of Al are known to enter the tetrahedral site for Si. Important localities include Franklin, New Jersey, USA in a metamorphosed, zinc stratiform ore body, and the Olympic peninsula, Washington, USA. Cf., armbrusterite, parsettensite, pyrosmalite, innsbruckite, varennesite



bentonite see Part 1 of Glossary



bergseife see "bole", halloysite



berthierine a member of the serpentine group with an ideal composition of approximately (Fe2+, Mn2+, Mg)3-x (Fe3+, Al)x (Si2-xAlx)O5(OH)4. Berthierine is commonly found in unmetamorphosed sedimentary iron formations. Berthierine occurs more commonly as either an apparent trigonal (possibly 1T) or less commonly as an apparent monoclinic (possibly 1M) polytype, and both polytypes are generally intergrown. Berthierine is often confused in the older literature with chamosite, a member of the chlorite group, but not to be confused with berthierite, a sulfide mineral. Cf., brindleyite, chamosite



bildstein an obsolete term for pyrophyllite or a mixture with dominant pyrophyllite

biotite defined by Rieder et al. (1998) as a trioctahedral mica between, or close to, the annite-phlogopite (i.e., ferrous iron and magnesium substitutions) and siderophyllite-eastonite (i.e., Al rich) joins. The term grandfathers the use of "biotite" in the field, when a chemical analysis is unavailable to describe a dark mica, presumably without Li.

birnessite a layered manganese oxide mineral (phyllomanganate) similar in structure to chalcophanite. The formula of a synthetic sample used in a structure determination (Post and Veblen, 1990) is Mg0.29Mn4+1.42Mn3+0.58O4 . 1.7H2O, assuming no Mn vacancies and an analysis total of 100%. Chalcophanite has a sheet of edge sharing Mn-O octahedra where one in seven octahedra is vacant. Zn cations are located above and below the vacant sites, also in octahedral coordination, with oxygen atoms from the octahedral sheet and from a plane of H2O molecules between the Mn-O sheets. Interlayer cations in birnessite, Mg, Na, K, Ca, etc., may occupy the Zn site and/or H2O sites (as found in chalcophanite). However, distributions of the interlayer cation and H2O sites in birnessite may also differ for various compositions (e.g., Na- vs Mg-rich birnessite), and the occupancy of the interlayer cation/H2O sites is believed to produce observed superstructures. Cation exchange and redox reactions can occur in birnessite. Ranceite is the (interlayer cation) Ca end member of birnessite and takanelite has Mn2+ as the interlayer cation. "Buserite" is a hydrated form of birnessite with a 10- spacing instead of the 7- value of birnessite. "Buserite" has not been found in nature and is not a mineral, but is a common phase during synthesis of birnessite. Birnessite is a major Mn-rich phase in many soils, in desert varnish, in ocean manganese nodules, and as an alteration product in Mn-rich ore deposits. Australian soils containing birnessite may be related to neutral to slightly alkaline conditions, but this result is not universal and the presence of birnessite may instead be related to a paucity of Ca and Mg of these soils.



biaxial mica an obsolete term for muscovite



bityite A trioctahedral member of the brittle mica group. The end-member formula is: CaLiAl2(BeAlSi2)O10(OH)2. Compositional range restriction includes viLi > vi, where = vacancy (i.e., viLi < vi is defined as margarite). Bityite forms in the 2M1 polytype and has been found in pegmatites from Madagascar, Zimbabwe, and the Urals, and in a tin vein in Uganda. Like margarite, bityite (Lin and Guggenheim, 1983) has nearly complete tetrahedral ordering of Al,Be vs Si, and thus is non-centric in symmetry (Cc space group). Cf., margarite



bixbyite Bixbyite, alpha-(Mn3+,Fe3+)2O3, is structurally comprised of edge sharing and corner sharing (Mn,Fe)O6 octahedra. Bixbyite has been reported from non-metamorphosed sediments where it had transformed from todorokite-birnessite, and from hydrothermal and low grade metamorphic deposits.



boehmite Boehmite, or gamma-AlO(OH), is a hydrous aluminum oxide comprised of corrugated sheets of double edge-sharing octahedra of Al-O,OH. Boehmite is isostructural with lepidocrocite, the Fe analogue. Bauxite is a mixture of diaspore, gibbsite, and boehmite, and any one of the three may dominate. Syn., böhmite



böhmite see boehmite



bole an obsolete term for a greasy clay with iron oxide impurities that produce a red, yellow and/or brown color and with about 24% water, possibly primarily halloysite. Syn. "bergseife" for "mountain soap", also obsolete



borocookeite a boron-rich member of chlorite with an ideal chemical composition of Li1+3xAl4-x (BSi3)O10(OH,F)8 where x = 0.0 to 0.33 atoms per formula unit (Zagorsky et al., 2003). Borocookeite occurs as the Ia polytype. Borocookeite has been found in miarolitic cavities at temperatures greater than 240-265 oC in pegmatite deposits, such as in the Krasny Chikoy district, Chita region, Russia. Cf., manandonite, boromuscovite



boromuscovite a dioctahedral member of the true mica group. The end-member formula is KAl2BSi3O10(OH)2, where = vacancy. Boromuscovite occurs as 2M1 and 1M polytypes and has been found in pegmatites at the eice pegmatite dikes, Czech Republic, where it occurs as fine-grained masses, and Little Three Mine pegmatite dike, San Diego County, California, USA, where it occurs as coatings from late-stage hydrothermal fluids. Cf., borocookeite, manandonite, muscovite



bowenite a transparent, yellow green variety of massive serpentine (antigorite?), used as an alternative for jade. Bowenite is not a mineral name and should not be used in the scientific literature. Syn. tangiwaite or tangawaite (from New Zealand)



bowleyite an obsolete term for bityite



bowlingite an obsolete term for a saponite-rich material from near Bowling, Dumbarton, Scotland



brammallite an aluminum-rich dioctahedral mica that shows interlayer deficiency and limited substitutions of Al in the tetrahedral sites. It is a series name (Rieder et al., 1998) with a generalized composition of Na0.65Al2Al0.65Si3.35O10(OH)2. Series names designate that additional research may be warranted.



brandisite an obsolete varietal term for clintonite



bravaisite a poorly defined material, possibly illite and montmorillonite



brindleyite a platy serpentine with an ideal composition of (Ni1.75Al1.0)(Si1.5Al0.5)O5(OH)4. Crystals are generally poorly crystalline mixtures of hexagonal and monoclinic polytypes. Poorly described, Al-rich material similar to a Ni analogue of amesite (referred to as "nimesite") was redefined as brindleyite. Brindleyite is compositionally similar to berthierine because of the tetrahedral Si/Al ratio and structurally similar owing to the hexagonal and monoclinic polytype intergrowths. Brindleyite has been found in the Marmara bauxite deposit, Greece. Cf., amesite, berthierine, garnierite, nepouite, pecoraite, pimelite, willemseite



brinrobertsite a regularly ordered interstratification of a pyrophyllite-like layer and dioctahedral smectite-like layer in a ratio of 1:1 (Dong et al., 2002) Cf., interstratification



bronzite (Finch) an obsolete varietal term for clintonite



brown mica an obsolete name for astrophyllite



brucite Brucite is a hydroxide mineral with the composition of Mg(OH)2. Also, brucite has been used as a group name for M2+(OH)2 where M = Fe, Mg, Mn, Ni. Brucite is comprised of a plane of Mg cations, with each Mg octahedrally coordinated by edge-sharing OH groups, thus forming an infinite two-dimensional sheet. Brucite primarily occurs as a contact metmorphic mineral in dolomites and Mg-rich limestones from the alteration of periclase, and in serpentinites and chlorite schists.



brunsvigite an obsolete varietal term for manganoan zincian chamosite. See chlorite



buddingtonite an ammonia-dominated feldspar mineral, NH4(Si3Al)O8. . Cf., alkali feldspar, feldspar, plagioclase feldspar



buldymite a poorly defined material, possibly biotite and vermiculite or interlayer-deficient biotite



bulgakite see astrophyllite group



buserite a synthetic phase, see birnessite





bytownite see plagioclase feldspar



chabazite see zeolite



caesium-biotite an obsolete varietal term for biotite



cairncrossite see reyerite group



calciobiotite an obsolete varietal term for biotite



calciotalc an obsolete varietal term for clintonite



cathkinite an obsolete term for a chocolate-brown saponite-rich material from Cathkin Hills, Scotland



carlosturanite Carlosturanite is a rare antigorite-like mineral that apparently contains vacant tetrahedral sites which interrupt the continuity of the tetrahedral sheet without affecting the continuity of the octahedral sheet (Mellini et al., 1985). The structure is thus similar to a modulated serpentine. To maintain charge balance, OH groups substitute for O atoms. The generalized formula is M21[T12O28(OH)4](OH)30.H2O, where M = Mg, Fe3+, Mn2+, Ti4+, and Cr3+, and T = Si, Al. Alberico (1998) showed that there are problems with the model of Mellini et al. (1985), and suggested the need to reexamine the structure. Important occurrences are related to low grade metamorphic (serpentinite) environments. Cf., antigorite



carrboydite see hydrotalcite group



caryopilite a modulated layer silicate based on the serpentine structure, with an approximate ideal composition of Mn2+3Si2O5(OH)4. Fe, Mg, and Al can substitute for Mn. There is an apparent excess of Si and an apparent deficiency in octahedral composition on the basis of 7 oxygen atoms. Earlier literature sometimes described caryopilite as bementite, but it has been shown that they are separate species. A monoclinic polytype is dominant and small amounts of a trigonal phase are often intergrown. Caryopilite, like greenalite, is an "island" structure where Si-rich tetrahedra of a given layer have apical oxygen atoms coordinate to one octahedral sheet and others to the adjacent sheet (Guggenheim and Eggleton, 1998). The islands are saucer-shaped with some islands inverted, and the islands are domed. Island diameters depend on composition with larger-diameter islands having smaller average octahedral cation sizes (4 tetrahedral-ring diameters in greenalite, 3 rings in caryopilite). Island domains are randomly displaced within layers. "Baumite", a mixture of several phases, contains a phase, probably Zn,Mg-rich, that is intermediate in domain structure to greenalite and caryopilite. Caryopilite is commonly found in bedded manganese deposits, such as those at the North Chichibu belt in the Shikoku region, SW Japan. Cf., greenalite



caswellite a poorly defined material, possibly mica and manganoan andradite



cat gold an obsolete term for muscovite



cat silver an obsolete term for muscovite



cataspilite a poorly defined material, possibly alteration product with dominant muscovite



catlinite a poorly defined material, possibly muscovite and pyrophyllite



celadonite a dioctahedral member of the true mica group. The ideal end-member formula is KFe3+(Mg, Fe2+)Si4O10(OH)2, where = vacancy. The typical range in composition is: viR2+/(viR2+ + viR3+) 0.25, viAl/(viAl + viFe3+) < 0.5, Mg/(Mg + viFe2+) > 0.5 (Rieder et al., 1998). Celadonite is commonly an alteration product of pyroxenes and other Fe,Mg minerals found in basalts either during low-grade metamorphism or hydrothermal activity.



celsian a Ba-dominated feldspar mineral, Ba(Si2Al2)O8. Cf., alkali feldspar, feldspar, plagioclase feldspar



cerolite equivalent to kerolite, see kerolite



chacaltaite a poorly defined material, possibly an illite pseudomorph after cordierite



chacaltocite an obsolete term for muscovite



chalcedony Chalcedony is a rock term to describe a mixture of a fibrous [110] variety of microcrystalline (length fast) quartz and moganite. Cf., quartzine



chalcodite an obsolete varietal term for stilpnomelane



chalcophanite see birnessite



chamosite the Fe-rich member of the chlorite group with a composition of ideally Fe2+5Al (Si3Al)O10(OH)8. There may be considerable substitutions of Mg, Fe3+, and Al for Fe2+. The common polytype is the IIb form, a one-layer form. Chamosite is an important constituent in oolitic and sedimentary iron formations and may be found as grain coatings in sandstones. See chlorite



chernykhite a dioctahedral member of the brittle mica group. The end-member formula is: BaV2Al2Si2O10(OH)2, where = vacancy, but known samples are deficient in Ba (or K). Typical site substitutions primarily occur in the octahedral site by Al, Fe, and/or Mg. The 2M1 polytype is the common polytype. Chernykhite is only known from southern Kazakhstan. Cf., roscoelite



chert Chert is a rock term to describe an authigenic species of SiO2 which consists of nanoscale intergrowths of quartz and moganite, a metastable SiO2 polymorph (Heaney, 1994). Cf., moganite, quartz



chlorite/smectite (or chlorite-smectite) terminology commonly used to denote the interstratification of chlorite or chlorite-like layers with smectite or smectite-like layers. Alternatively, this interstratification can be described as chlorite/corrensite. It may be abbreviated as C/S or C-S. Because the interstratification is not regular, it is not recognized as a unique phase. Cf., chlorite, corrensite, smectite



chlorite a group name for phyllosilicates with the general formula of (R2+6-y-z R3+y z) (Si4-x R3+x)O10(OH)8 where represents vacancies, x is the number of tetrahedral R3+ cations, y is the number of octahedral R3+ cations, and z is the number of vacancies. The common structure consists of negatively charged trioctahedral 2:1 layers alternating regularly with positively charged trioctahedral interlayer sheets. Ideal composition of the 2:1 layer is (R2+, R3+)3 (Si4-x R3+x)O10(OH)2 and that of the interlayer is (R2+, R3+)3(OH)6. Bayliss (1975) defined trioctahedral end members based on the dominant cation, e.g., Fe-rich, chamosite; Mg-rich, clinochlore; Mn-rich, pennantite; Ni-rich, nimite; Zn-rich, baileychlore. The trioctahedral chlorites are commonly found in metamorphic rocks and are the diagnostic mineral of the greenschist facies. Chlorite is also a common alteration product. Eggleton and Bailey (1967) combined composition and structure characteristics to define dioctahedral chlorite species. Cookeite is the Li-rich chlorite, whereas sudoite is essentially Li-free. Cookeite and sudoite occur in pegmatite, hydrothermal deposits, and ore deposits. Both have a dioctahedral 2:1 layer and a trioctahedral interlayer (di, trioctahedral chlorite). Donbassite has two dioctahedral sheets (di,dioctahedral chlorite) and is Al-rich. For trioctahedral chlorite, the common polytype is the one-layer, IIb form, although cookeite, commonly forms in the one-layer Ia form (cf., Ia polytype, IIb polytype). See also Part 1 of the Glossary.



chlormagaluminite see hydrotalcite group



chloropal an obsolete term for nontronite



chlorophanerite an obsolete term for glauconite



chlorophœite a poorly defined material, found as infillings in cavities in basic igneous rocks, possibly an altered chlorite



chrombiotite an obsolete varietal term for biotite



chromceladonite a dioctahedral member of the true mica group. The ideal end-member formula is KCrMg(Si4O10)(OH)2 where = vacancy. First discovered at the Srednyaya Padma U-V deposit, chromceladonite was described from southern Karelia, Russia, in occurrences relating to apparent metasomatism and in association with dolomite, calcite, hematite, quartz, roscoelite, chromphyllite, uraninite, zincochromite, vanadium oxides and selenides (Pekov et al., 2000). Chromceladonite occurs as a 1M polytype. Cf., chromphyllite



chrome mica an obsolete term for chromian muscovite, chromian phengite



chromglimmer an obsolete term for chromian muscovite, chromian phengite



chromochre an obsolete term for chromian muscovite



chromphyllite a dioctahedral member of the true mica group. The ideal end-member formula is KCr2AlSi3O10(OH,F)2, where = vacancy. Chromphyllite, like muscovite, occurs as the 2M1 polytype in C2/c symmetry, and the Cr forms a solid solution series with Al in muscovite. Chromphyllite is known from the Lake Baikal region, Russia, Outokumpu, Finland, and elsewhere, and is believed to occur in association with metasomatism. Cf., muscovite



chrysophane an obsolete term for clintonite



chrysotile a member of the serpentine group with textures showing packets of cylinders, scrolls, and tubes, as well as helical or spiral fibers. Chrysotile, ideally Mg3Si2O5(OH)4, crystallizes in monoclinic symmetry (clinochrysotile) with the fiber axis parallel to X and orthorhombic symmetry with the fiber axis along X (orthochrysotile) or Y (parachrysotile). Polytype stacking for clinochrysotile is either 2Mc1 or 1Mc1, where the number of layers (e.g., 1 or 2) precedes M = monoclinic, subscript c = cylindrical, and subscript 1 is used to distinguish the form from another cylindrical polytype that would otherwise have the same symbol. The orthochrysotile polytype is 2Oc1. Cylindrical structures do not have consistent hydrogen bonding between layers that would be observed in an ideal platy structure, and thus do not conform to the standard polytypes. Fiber dimensions are variable with inner diameters near 70-80 and outer diameters reported at 220-270, >350, and 490 (the latter value involves synthetic samples). Al, Fe2+, and Fe3+ may substitute for Mg, and Fe3+ may substitute for Si; all substitutions are very limited, but greater than in lizardite. The differences between these substitutions in lizardite vs. chrysotile suggest that in natural systems, lizardite and chrysotile are not sensu stricto polymorphs. Chrysotile, or "white asbestos", is the asbestosform serpentine and is mined in Russia near the Ural Mountains and in Asbestos, Quebec, Canada.



clingmanite an obsolete term for margarite



clinochlore the trioctahedral Mg-rich member of the chlorite group. See chlorite



clinoenstatite a monoclinic (P21/c) polymorph of enstatite. It is a product of fast cooled protoenstatite. Clinoenstatite occurs in Mg-rich basaltic rocks.



clinoptilolite see zeolite



clinopyroxene a pyroxene subgroup of Ca-,Na-bearing pyroxenes with monoclinic (C2/c, P21/c) symmetry. See pyroxene group for additional details.



clinotobermorite see tobermorite



clintonite a trioctahedral member of the brittle mica group. The end-member formula is: CaMg2Al(Al3Si)O10(OH)2. Typical site substitutions include: Ca > Na,K; Fe2+, Al, Fe3+, Mn for Mg; and Al and Fe3+ for Si or ivAl. The common polytype is 1M, and the 2M1, 1Md, and 3T are rare. The Loewenstein Al avoidance rule is violated in that the tetrahedral content of Al3Si requires that Al tetrahedra share bridging oxygen atoms with other Al tetrahedra, which is unusual in aluminosilicate minerals. Clintonite occurs in metasomatically altered limestones, which involves thermal metamorphism coupled with a restrictive bulk composition undersaturated in silica.



coalingite see hydrotalcite group



colomite an obsolete term for roscoelite



common mica an obsolete term for muscovite



confolensite an obsolete, local term for montmorillonite from Confolens, Charente, France



connarite an obsolete varietal term for willemseite



cookeite a Li-bearing member of the chlorite group, with an ideal composition of (Li,Al4)(Si3Al)O10(OH)8. The octahedral sheet of the 2:1 layer is dioctahedral and the interlayer is trioctahedral, therefore this is a di,trioctahedral chlorite. The common polytype is based on the Ia structure. Cf., chlorite



coombsite see zussmanite



coronadite see hollandite



corrensite a regular interstratification of trioctahedral chlorite-like layers with either trioctahedral smectite-like or trioctahedral vermiculite-like layers, the former being "low-charge corrensite" and the latter "high-charge corrensite". The ratio of chlorite-like layers to smectite-like or vermiculite-like layers is 1:1 (Guggenheim et al., 2006). Corrensite occurrences are from low temperature environments, such as evaporites, saline deposits, sedimentary rocks, weathering zones, hydrothermal systems, burial diagenesis, low grade metamorphic regimes, and some contact metamorphic zones. Beaufort et al. (1997) discussed corrensite possibly as a regular mixed-layer structure involving a continuous series from smectite (or vermiculite) to chlorite or alternatively, as a single phase with a regular alteration of chlorite and smectite (or vermiculite) layers, with a stability field. If the latter, mixtures that deviate from 1:1 ratios of interstratified layers would require physical mixtures of appropriate layers of corrensite and chlorite.



corundellite an obsolete term for margarite



corundophilite an obsolete term for low-Si (and variable amounts of Fe2O3) chlorite



cossaite an obsolete varietal term for paragonite



cristobalite Beta-cristobalite, a high temperature (above 1470 oC, but below liquid at 1727 oC at 1 bar) polymorph of SiO2, has an ideal basic structure that is polytypic with tridymite. Like tridymite, beta cristobalite has sheets of hexagonal tetrahedral rings with alternate tetrahedra around a ring with apices pointing in opposite directions from adjacent tetrahedra. These sheets have an ABCABC... stacking sequence, which creates an offset such that no channels form as they do in tridymite. Cristobalite is found in volcanic rocks, primarily in a fine groundmass, but also as a lining of cavities and as a devitrification of volcanic glasses. Cf., opal, tridymite, quartz



cronstedtite Cronstedtite is the Fe-rich serpentine of composition (R2+3-xFe3+x)(Si2-xFe3+x) O5(OH)4. Divalent cations (R2+) may include Fe, Mg, Mn, and possibly Ca. It is assumed that the value of x in the formula is equal (and near 0.5 to 1.0) for both the tetrahedral and the octahedral sites. Cronstedtite has a large number of polytypes, with the 1T (space group P31m) most common. The lateral dimensions of the iron-rich tetrahedral sheet are large, but the lateral dimensions of the octahedral sheet are large also, and thus tetrahedral rotation ranges only up to ~8 o. Because most (possibly all) of the iron is ferric, the tetrahedral-octahedral misfit is limited. Fe3+ and Si segregate to different T sites in the 2H2 polytype, but not in the 1T, 3T, 2H1, and 6R2 polytypes. Amesite-2H2 also shows tetrahedral ordering, but between Al and Si. Cronstedtite forms in low-temperature hydrothermal veins with other iron rich minerals, such as siderite, and in low-temperature metamorphosed iron formations. It is also known to occur in carbonaceous chondrites. The Mn analogue of cronstedtite is guidottiite. Cf., amesite, greenalite, guidottiite



cryophyllite an obsolete varietal term for zinnwaldite, ferroan trilithionite, and ferroan polylithionite



cryptomelane see hollandite



culsageeite an obsolete name for altered material, probably vermiculite



cymatolite a poorly defined material, possibly muscovite and albite



damourite an obsolete term for muscovite



daphnite an obsolete term for a low-Si chlorite



delessite an obsolete term for a chlorite material, rich in ferric iron, probably a Mg-rich chamosite



de saulesite a discredited term for pimelite



desautelsite see hydrotalcite group



devitoite see astrophyllite group



deweylite an obsolete term for a mixture of poorly crystalline phyllosilicates (1:1 and 2:1 types). When red, "deweylite" was called "eisengymnite", and when found at Bare Hills, Maryland, USA, "deweylite" was called "gymnite".



diabantite a discredited term for a Si- and Fe-rich (clinochlore) chlorite



diaspore a polymorph of hydrous aluminum oxide, lpha-AlO(OH), and isostructural with goethite, lpha-FeO(OH). The structure is comprised of double chains of edge-sharing octahedra of AlO3(OH)3 along the c axis, and the chains are offset along the b axis. Diaspore occurs with corundum, often in chlorite schists and in dolomite, and as a major constituent as fine-grained matrix in bauxite.

dickite a member of the kaolin group, which consists of the dioctahedral and aluminous rich 1:1 phyllosilicates. Dickite has a chemical composition of Al2Si2O5(OH)4. Dickite is distinguished from the other polymorphs, kaolinite and nacrite, by the vacant octahedral site regularly alternating from layer to layer across "B" and "C" sites. Thus, the polytype is a two layer form with monoclinic symmetry, Cc. The "B" and "C" sites would be related by a mirror plane if both sites were occupied identically within the same layer, whereas the "A" site resides on the mirror plane (Bish and Johnston, 1993). Dickite has a widespread occurrence and often is believed to be transformed from kaolinite (and therefore dickite is the more stable phase) by higher temperature (various temperatures have been suggested depending on origin, e.g., ~120 oC, 290 - 300 oC, 80 - 160 oC), but dissolution-precipitation of kaolinite to dickite has been suggested also, as well as direct precipitation. Dickite has been described from hydrothermal and diagenetic environments. Examples of hydrothermal dickite include those of Japan and Nayarit, Mexico. Cf., halloysite, kaolin, kaolinite, nacrite



didrimite an obsolete term for muscovite



didymite an obsolete term for muscovite



diopside a clinopyroxene with an end-member composition of CaMgSi2O6. A continuous solid-solution series exists between diopside and hedenbergite, CaFeSi2O6. Diopside occurs in metamorphic rocks, alkali basalts, and nodules in kimberlite. Near end-member diopside occurs in metasomatic rocks, such as skarns formed through contact metamorphism between siliceous carbonate and granitic intrusion. See pyroxene group for additional details



diphanite an obsolete term for margarite



disterrite an obsolete varietal term for clintonite



donbassite a member of the chlorite group, with an ideal formula of (Al 4+x/3Si4-xAlx)O10(OH)8, where x represents excess Al. Both octahedral sheets are dioctahedral, therefore this is a di,dioctahedral chlorite. Cf., chlorite



dozyite a regular interstratification of trioctahedral serpentine with trioctahedral (i.e., tri,trioctahedral) chlorite. The ratio of chlorite layers (i.e., one 2:1 layer and one interlayer) to serpentine (i.e., one 1:1 layer) is 1:1. The name applies to any composition of interstratified trioctahedral serpentine or trioctahedral chlorite regardless of the structure type (i.e., stacking) of the chlorite. Variations in chemical composition other than Mg and Al may be noted by descriptive adjectival modifiers (Bailey et al., 1995).



dudleyite a poorly defined material, possibly smectite or vermiculite



dysintribite an obsolete term for muscovite



eastonite a trioctahedral member of the true mica group. The ideal end-member formula is KMg2Al(Al2Si2)O10(OH)2, although such a chemical composition has not been reported. The original eastonite occurrence from Easton, Pennsylvania, USA, was shown to be a mixture of phlogopite and lizardite-1T with some "antigorite-like offsets". The eastonite composition is useful to describe solid solution series where there are Mg + Al substitutions. Cf., presiwerkite, siderophyllite



eggletonite see ganophyllite



eisengymnite see "deweylite"

ekmanite a 2:1 modulated phyllosilicate having an ideal chemical composition of KM20Si32O76(OH)17, where M = Fe2+, Mg, Mn2+. Analyses show that Ca and Na substitutes for K, Fe3+ substitutes for M, and Al substitutes for Si. Ekmanite has a highly disordered layer-stacking. The proposed model (Ferrow et al, 1999), based on TEM analysis, has strips of tetrahedra attached to the continuous octahedral sheet, with the strips along the a axis. The basic layer is 2:1 with inverted tetrahedra linking across the interlayer through apical oxygen atoms, with three of eight tetrahedra linking the 2:1 layers and inverted relative to adjacent octahedral sheets, similar to bannisterite. All tetrahedral rings are 6-fold, unlike bannisterite. Ekmanite is known from the magnetite ore body and skarns at Brunnsjögruvan, Sweden, in rocks metamorphosed to greenschist facies.



elhuyarite an obsolete term for allophane associated with lignite from Friesdorf, Germany



emerylite an obsolete term for margarite



endellite a redundant term for halloysite and its use should be discontinued



enstatite an orthorhombic (space group Pbca) pyroxene, with an end-member composition of Mg2Si2O6. Enstatite and ferrosilite, Fe2Si2O6, form a continuous solid solution series (with <5 mole % of CaSiO3). Enstatite commonly occurs in mafic and ultramafic igneous rocks and some high-grade metamorphic rocks (granulite facies). Polymorphs of enstatite include a low-temperature, monoclinic form (clinoenstatite) and a high-temperature, orthorhombic form (protoenstatite) that may also occur naturally in nanocrystallite form. Ca-rich exsolution lamellae in enstatite crystals are common. See pyroxene group for additional details.



ephesite a trioctahedral member of the true mica group. The end-member formula is NaLiAl2(Al2Si2)O10(OH)2. Ephesite occurs as the 1M and 2M1 polytypes. Ephesite has been identified in pegmatite as a hydrothermal alteration product with analcime and natrolite from the Ilimaussaq intrusion, Greenland, and in manganese ore from Postmasburg, South Africa.



epichlorite a poorly defined material, possibly an altered chlorite



epileucite a poorly defined material, possibly a muscovite and K-rich feldspar pseudomorph after cordierite



episericite a poorly defined material, possibly illite



erionite see zeolite



errite an obsolete (light green) variety of parsettensite



ettringite see calcium silicate hydrate (CSH) in Part 1

eukamptite a poorly defined material, possibly altered biotite



euchlorite an obsolete term for biotite



euphyllite a poorly defined material, possibly paragonite and muscovite or paragonite



euralite a poorly defined material, possibly an altered chlorite found as infillings in cavities in basic igneous rocks



falcondoite a member of the palygorskite-sepiolite group with a composition of approximately (Ni8-y-z R3+yz) (Si12-x R3+x) O30 (OH)4 (OH2)4 . R2+(x-y+2z)2 (H2O)8, where R is a cation, are vacancies, and x, y, and z are compositional parameters. See palygorskite-sepiolite group



faratsihite a poorly defined material, probably a mixture of kaolin and nontronite



fedorite see reyerite group



feitknechtite see groutite



feldspar The group name for a set of anhydrous framework silicate minerals. The most common feldspar minerals belong to the ternary system of end members of albite [Ab: Na(Si3Al)O8], anorthite [An: Ca(Si2Al2)O8], and orthoclase [Or: K(Si3Al)O8]. Si and Al atoms are in tetrahedral sites of the aluminosilicate framework. Large monovalent or divalent cations (Na, K, Ca, Ba) occupy interstices of the framework to maintain charge balance. In general, cleavage along the {001} is perfect and good on the {010} planes. The feldspar group minerals are separated into two series, alkali (K- to Na-rich) feldspars and plagioclase (Na- to Ca-rich) feldspars. At high temperature, solid solutions are common in both alkali feldspar (between K and Na) series and plagioclase feldspar (between Na and Ca, and Si and Al) series, but not between K- and Ca-rich feldspars. During cooling, homogeneous compositions may exsolve to form perthite (alkali feldspar with plagioclase exsolution) or antiperthite (albite with "orthoclase" exsolution). Feldspar minerals readily weather near the surface of the earth to produce clay minerals. In addition, ground feldspar and quartz may be mixed with clays and/or clay minerals (e.g., kaolin) and fused to create porcelain and glazes, with the feldspar acting as a binder material. Cf., alkali feldspar



Fe muscovite an invalid name for a hypothetical end member



feroxyhite a poorly defined, fine grained, poorly crystalline, and non-magnetic form of gamma-FeO(OH). Feroxyhite transforms in air to goethite, but it has been found in ocean-floor iron-manganese concretions and in some soils with high iron hydroxide content. Drits et al. (1993) examined several structural models and suggested from X-ray data that iron atoms occupy octahedral sites with distributions of face-sharing octahedral pairs alternating with vacant octahedral pairs along the c axis. Syn., feroxyhyte



ferri-phengite an obsolete varietal term for ferrian muscovite



ferriannite an obsolete term for tetra-ferri-annite



ferribiotite an obsolete varietal term for biotite



ferrihollandite see hollandite



ferrihydrite Ferrihydrite is metastable, fine grained, and poorly crystalline and occurs as brown gel-like precipitates and as friable crusts in soil matrix in podzols or lithosols, and in environments associated with acid mine drainage. The chemical composition of ferrihydrite is very approximately Fe2O3 . 2FeO(OH) . 2.6H2O, and it is believed to be a precursor of hematite and possibly goethite (by dissolution). Surface adsorption of organic molecules and (heavy and other foreign) metals may occur and affect ferrihydrite stability. The gel-like forms, when studied by powder X-ray diffraction, produces patterns with two broad diffraction peaks ("two line ferrihydrate") and the crust produces five or more lines ("five line ferrihydrate" and sometimes as "six line ferrihydrate"). Ageing promotes formation of the "five line ferrihydrite" from the two line form. Michel et al. (2007) suggested a single-phase model for ferrihydrite that is based on a cluster of 13 Fe and 40 oxygen atoms: central FeO4 tetrahedra surrounded by 12 FeO6 octahedra, with an ideal chemical composition of Fe10O14(OH)2. The model is affected by surface bound H2O, surface effects, strain and defects, particle size and shape, etc.



ferrimuscovite an invalid name for a hypothetical end member



ferriphlogopite an obsolete varietal term for ferrian phlogopite, tetra-ferriphlogopite



ferripyrophyllite the ferric iron analogue of pyrophyllite



ferrisepiolite a member of the palygorskite-sepiolite group with a composition of approximately (Fe3+,Fe2+,Mg)4 (Si,Fe3+)6 O15(O,OH)2 . 6H2O. See palygorskite-sepiolite group



ferristilpnomelane see stilpnomelane



ferrititanbiotite an obsolete varietal term for biotite



ferriwodanite an obsolete varietal term for biotite



ferriwotanite an obsolete varietal term for biotite



ferro-aluminoceladonite a dioctahedral member of the true mica group. The end-member formula is K Al(Fe2+,Mg)Si4O10(OH)2. Typical range in composition is: viAl/(viAl + viFe3+) = 0.5 - 1.0, Mg/(Mg + viFe2+) 0.5 (Rieder et al., 1998). Li et al. (1997) described ferro-aluminoceladonite-1M from tuffs in the Murihiku Supergroup, Hokonui Hills, Southland, New Zealand.



ferro-ferri-muscovite an obsolete term for ferrian annite



ferro-phlogopite an obsolete varietal term for ferroan phlogopite



ferroceladonite A dioctahedral member of the true mica group. The end-member formula is K Fe3+(Fe2+, Mg,)Si4O10(OH)2. Typical range in composition is: viAl/(viAl + viFe3+) < 0.5, Mg/(Mg + viFe2+) 0.5 (Rieder et al., 1998). Li et al. (1997) described ferroceladonite-1M from tuffs in the Murihiku Supergroup, Hokonui Hills, Southland, New Zealand.



ferroferrimargarite an obsolete varietal term for margarite



ferrokinoshitalite a trioctahedral member of the brittle mica group with an ideal chemical composition of BaFe2+3Si2Al2O10(OH)2. Ferrokinoshitalite occurs as a 1M polytype from the silicate-rich bands of high-grade metamorphic rocks in banded iron formation at the Broken Hill massive sulfide deposit, Namaqualand metamorphic complex, northern Cape Province, South Africa (Guggenheim and Frimmel, 1999). The Si and Al are disordered in the tetrahedral sites.



ferromuscovite an obsolete varietal term for biotite



ferrophengite an invalid name for a hypothetical end member



ferrophlogopite an obsolete varietal term for ferroan phlogopite



ferropyrosmalite see pyrosmalite



ferrosilite an orthorhombic (space group Pbca) pyroxene, with an end-member composition of Fe2Si2O6. End-member ferrosilite does not occur under normal pressure conditions, with the assemblage of fayalite and quartz thermodynamically more stable than ferrosilite. Ferrosilite is thus rare, but it has been found in mafic rocks and some high-grade metamorphosed banded iron formations. See pyroxene group for additional details.



ferrosilite III see pyroxenoid group



ferrostilpnomelane see stilpnomelane



flogopite an obsolete term for phlogopite



fluortainiolite an obsolete term for tainiolite



foshagite see tobermorite



fraipontite the Zn-rich, platy serpentine defined ideally as Zn3(Si,Al)2O5(OH)4. Cu, Al, and vacancies are known to substitute for Zn. Occurrences include Gleeson, Arizona, USA, and Laurion, Greece (both Cu-rich), Defiance, Belgium, and Tsumeb, Namibia.



franklinfurnaceite an intermediate structure between chlorite and brittle micas (Peacor et al., 1988). The franklinfurnaceite structure is similar to chlorite-IIa-1 polytype with a trioctahedral 2:1 layer, but with a dioctahedral interlayer (thus, tri-dioctahedral). It differs from chlorite and is more mica-like because Ca cations occupy octahedral sites between the tetrahedral sheets and the dioctahedral interlayers. Franklinfurnaceite is ideally Ca2Fe3+Mn2+3Mn3+[Zn2Si2O10](OH)8 and occurs at Franklin, New Jersey, USA.



franklinphilite the Mn analogue of stilpnomelane, see stilpnomelane



frauenglas an obsolete term for muscovite



friedelite see pyrosmalite



fuchsite an obsolete term for chromian muscovite



gaebhardite an obsolete term for chromian muscovite



galapectite an obsolete term for a halloysite from Angleur, Belgium



ganophyllite a modulated 2:1 layer silicate with a continuous octahedral sheet and a tetrahedral sheet that involves triple chain strips linked by pairs of inverted tetrahedra that connect the strips and adjacent layers (Eggleton and Guggenheim, 1986). The ganophyllite chemical composition is approximately (K,Na,Ca)6(Mg,Fe,Mn)24(Si32.5Al7.5)O96(OH)16 . 21H2O. The large cations (K, Na, Ca) are exchangeable and occur associated near the undersaturated inverted tetrahedra that connect adjacent layers. Eggletonite is the Na analogue of ganophyllite. Ganophyllite occurs in low-grade metamorphic, silicate-rich manganese deposits, such as those found at the Harstig mine, Pajsberg, near Persberg, Vermland, Sweden.



ganterite a dioctahedral member of the true/brittle mica group with the ideal chemical composition of [Ba0.5(Na,K)0.5]Al2(Si2.5Al1.5O10)(OH)2. Ganterite may be described as a Ba-dominant analogue of muscovite-2M1 that crystallizes, like most muscovite crystals, in space group C2/c. Ganterite was originally described from basement rocks of the Berisal Complex, Simplon Region, Switzerland (Graeser et al., 2003). but it has also been found from Oreana, Nevada, and Ba-rich muscovite-like phases have been reported from West Greenland; Ontario, Canada; and Franklin/Sterling Hill, New Jersey, USA.



garnet a group of orthosilicate (= nesosilicate) minerals with stoichiometry of A3B2(SiO4)3, where divalent cations occur in the large-size (8-coordinated) A site and trivalent cations occur in the medium-size (6-coordinated octahedron) B site. Common garnet minerals are pyrope [Mg3Al2(SiO4)3], almandine [Fe3Al2(SiO4)3], spessartine [Mn3Al2(SiO4)3], uvarovite [Ca3Cr2(SiO4)3], grossular [Ca3Al2(SiO4)3], and andradite [Ca3Fe2(SiO4)3]. These garnets are separated into two series, pyralspite (the Mg, Fe, and Mn Al-rich members) and ugrandite (the Ca-rich members). Solid solution is common in the A site of pyralspite and in the B site of ugrandite, but little substitution between the two series. Grandite is a generic name for the grossular-andradite series. Garnet minerals commonly occur in metamorphic rocks, and are believed to be stable in the lower mantle of the earth. The minerals are generally cubic (= isometric) in symmetry. Garnet minerals are generally hard (Mohs hardness H: 6.5 to 7.5) and dense (specific gravity G: 3.5 to 4.5) and are used commercially as an abrasive. Syn., silicate garnet



garnierite Although not a valid mineral name, garnierite is often used as a field term for nickel-bearing (± magnesium) hydrous phyllosilicates.



gavite an obsolete term for a variety of talc that apparently deviates from the (OH) content of talc as determined in old literature, from Gava valley, Italy



genthite a discredited term, a mixture of pimelite and Ni-rich serpentine



gibbsite a polymorph of Al(OH)3 where one third of the octahedral sites are vacant and each OH group is coordinated by two Al cations. Although each layer is approximately closest packed, the stacking of layers is not closest packed, and OH groups in adjacent layers superpose. The interlayer OH to OH distance is relatively small (at ~2.78 ), indicating a strong hydrogen bond that is enhanced by strong polarization caused by the highly charged Al3+ cation. Cf., bayerite, nordstrandite



gibbsite-like a term that is synonymous with the dioctahedral interlayer sheet in chlorite. This sheet is analogous to gibbsite in that gibbsite consists of two (intralayer) planes of closest packed oxygen atoms with two out of three of the octahedral sites between the two planes occupied by trivalent cations, in this case Al. In the gibbsite-like sheet, some of the oxygen atoms are replaced by hydroxyl groups, (OH). This term is only for chlorite. The dioctahedral sheet in a 2:1 layer silicate, such as mica, is very different from gibbsite, whereas the interlayer in a chlorite is quite "gibbsite-like". For example, in a 2:1 layer octahedral sheet, two thirds of the oxygen anions are apical oxygen atoms whereas only one third are OH groups--very different from a gibbsite-like sheet.

glagolevite a chlorite-like mineral containing Na in seven-fold coordination located between the interlayer octahedral sheet and the 2:1 layer. The ideal chemical composition is Na(Mg,Al)6(Si3Al)O10(OH,O)8. Glagolevite was described by Krivovichev et al. (2004) in analogy to chlorite as a tri-trioctahedral chlorite with polytypes IIb-6, IIb-2 and IIb-4. The mineral occurs at the Kovdor Phlogopite quarry, Kovdor massif, Kola peninsula, Russia.



glauconite an iron-rich dioctahedral mica that shows K deficiency and limited substitutions of Al in the tetrahedral sites. Glauconite is a series name (Rieder et al., 1998) with a generalized composition of K0.8R3+1.33R2+0.67(Al0.65Si3.87)O10(OH)2, where viR2+/(viR2+ + viR3+) > 0.15, and viAl/(viAl + viFe3+) < 0.5 and shows no compositional overlap with celadonite. Often interstratified with smectite as the mixed-layered mineral glauconite/smectite. When mixed with other minerals or when referring to morphological features, the term "glauconitic" is appropriate. The mode of origin is not a criterion for identification.

goethite see diaspore



gigantolite a poorly defined material, possibly muscovite and cordierite



gilbertite an obsolete term for muscovite



goeschwitzite an obsolete term for illite



gonyerite a poorly known, modulated 2:1 layer silicate (Guggenheim and Eggleton, 1987). Although superficially resembling chlorite, gonyerite has a two-layer structure with structurally different types of interstratified layers. Inverted tetrahedra occur between the 2:1 layer and linked to the what would be the brucite-like interlayer in an ideal chlorite. Samples of gonyerite are generally impure, although an analysis by Frondel (1955) reported an approximate composition of (Mn3.25Mg1.95Fe3+0.64)(Si3.75Fe3+0.17Al0.08)O10.2(OH)7.8 and is based on the assumption that gonyerite is a chlorite and all iron is ferric. Gonyerite occurs in low-grade metamorphic, silicate-rich manganese deposits, such as that at the Harstigen Mine, Pajsberg, Värmland, Sweden.



graminite an obsolete term for nontronite



grandite see garnet



greenalite a modulated 1:1 layer silicate based on the serpentine structure, with an approximate ideal composition of Fe2+3Si2O5(OH)4. Mn, Mg, and Al can substitute for Fe. There is an apparent excess of Si and an apparent deficiency in octahedral composition on the basis of 7 oxygen atoms. Earlier literature erroneously described greenalite as an iron serpentine, similar to the structure of lizardite. The 1T polytype (space group P31m) is dominant and the 1M polytype (space group Cc) is often intergrown. Greenalite is an "island" structure where Si-rich tetrahedra of a given layer have apical oxygen atoms coordinate to one octahedral sheet and others to the adjacent sheet (Guggenheim and Eggleton, 1998). The islands are saucer-shaped with some islands inverted, and the islands are domed. Island diameters depend on composition with larger-diameter islands having smaller average octahedral cation sizes (4 tetrahedral-ring diameters in greenalite, 3 rings in the Mn analogue, caryopilite). Island domains are randomly displaced within layers. Greenalite is commonly found in Precambrian iron formations. Cf., caryopilite



griffithite a poorly described material, possibly chlorite, from Griffith Park, Los Angeles, California, USA



groutellite "Groutellite" is a poorly defined phase that had been found in heating experiments as an intermediate phase from ramsdellite to groutite with a possible composition of Mn2O3OH. The phase is a synthesis product only, although it has been anticipated that it may occur in nature.



groutite Groutite is a manganese oxyhydroxide, alpha-MnO(OH), and is isostructural with diaspore. The manganese is trivalent and coordinated with O to form edge-sharing Mn3+O6 octahedra, which are linked three-dimensionally by sharing vertices. The three dimensional structure is comprised of tunnels, with the sizes of these tunnels determined by the chain widths. In groutite, the edge-sharing octahedra form double chains, whereas in manganite (gamma-MnO(OH); isostructural with rutile) the edge-sharing octahedra form single chains. Jahn-Teller distortions (Kohler et al., 1997) affect the octahedral shape with four short and two long Mn-O bond lengths and determine partially where the hydrogen links the octahedral chains to form the overall topologies. Groutite may be described as a distorted derivative of ramesdellite (MnO2, with Mn4+ and a double octahedral chain; isostructural with gibbsite) and manganite as a distorted derivative of pyrolusite, beta-MnO2 (and a single octahedral chain with Mn4+; isostructural with rutile). Feitknechtite, beta-MnO(OH), has not been well described. Pyrolusite occurs in low temperature hydrothermal deposits and as replacement after other Mn oxide minerals. Groutite and ramesdellite are rare, often altering to pyrolusite, and occur in low temperature hydrothermal deposits. Feitknechtite occurs as fine-grained mixtures with hausmannite.



grovesite a discredited name, now known to be a Mn-rich chlorite, pennantite



grundite an obsolete term for illite



grüner Chrysopraserde an obsolete term for poorly described Ni- and Mg-rich phyllosilicates, generally characterized as "garnierite"



guidottiite the Mn-analogue of cronstedtite, a serpentine. Guidottiite has an ideal composition of (Mn2Fe3+)(SiFe3+)O5(OH)4. Guidottiite-2H1 and -2H2 were reported by Wahle et al. (2010) with random interstratified polytype intergrowths and stacking disorder common. The sample comes from the Kalahari Manganese field, South Africa, and forms from hydrothermal solutions.



gumbellite an obsolete term for illite-2M2



gymnite see "deweylite"



gyrolite see reyerite group



hallerite a poorly defined material, possibly paragonite and lithian muscovite



hallite an obsolete name for altered material, probably vermiculite



halloysite a member of the kaolin group, with a chemical composition of ideally

Al2Si2O5(OH)4 . x(H2O). Varying amounts (x) of H2O may be present in the interlayer, and the terms halloysite (7 Å) and halloysite (10 Å) were recommended for general usage to quantify the amount of H2O present between layers. Values of x ~ 0 [halloysite (7 )] are near kaolinite and x ~2 is halloysite (10 ). Gentle heating of the halloysite (10 ) phase will produce halloysite (7 ), and this is a non-reversible reaction. Halloysite (10 ) requires storage in water to prevent (partial) dehydration. Halloysite commonly has considerable stacking disorder although a "well crystallized" sample may have an approximate two-layer (2M1) structure for halloysite (7 ) for a limited stacking sequence of 6-7 layers. Atomic coordinates for interlayer H2O are not known, although H2O within the silicate ring and H2O in a discontinuous plane between the layers have been suggested. Halloysite layers may be planar, curved, rolled (tubular), and partly spherical to spherical, and these morphologies appear to be related to crystallization conditions and chemical composition. There is no way to conclusively differentiate between halloysite and kaolinite without knowing the history of the sample, although suggestions have included the evidence of the 2M1 polytype and various treatments involving intercalation as ways to identify halloysite (7 ). Cf., dickite, kaolin, kaolinite, nacrite



haughtonite an obsolete varietal term for biotite



hausmannite Hausmannite, Mn304, is tetragonal and has a deformed cubic spinel structure.

Each Mn cation (Jarosch, 1987) in octahedral coordination is affected by Jahn-Teller distortions with two long Mn-O distances and four short distances. The Mn-O4 tetrahedra have equal Mn-O bond lengths. Hausmannite is isostructural with the Fe3O4 inverse spinel structure (magnetite). Hausmannite occurs in metamorphic manganese deposits, for example at Langban, Sweden, and Postmasburg, South Africa.



hectorite Hectorite is the Mg- and Li-rich trioctahedral member of the smectite group. It has the ideal chemical composition of (M+y . nH2O)(Mg3-yLiy)Si4O10(OH)2 where M is the exchangeable cation, y is the Li content, and n is variable. The M (interlayer) cation is assumed here as univalent, but it may have other valence states also. F substitution for (OH) has been documented. Stacking of natural samples is generally turbostratic. Fluorohectorite, with M = Na, K, Rb, and Cs and with y = 0.5 was synthesized by Breu et al. (2003), and the well-ordered, one-layer structure of the Cs phase was determined (space group C2/m, 1M polytype). Cf., swinefordite



hedenbergite a clinopyroxene (monoclinic space group C2/c) with an end-member formula of CaFeSi2O6. Hedenbergite and diopside, CaMgSi2O6, form a continuous solid solution series. Hedenbergite primarily occurs in metamorphic rocks and skarns. See pyroxene group for additional details.



helvetan a poorly defined material, possibly decomposed biotite



hendricksite a trioctahedral member of the true mica group. The end-member formula is KZn3AlSi3O10(OH)2. The Zn content must be greater than or equal to 1.5 for the specimen name to be valid. Reported polytypes are 1M, 2M1, and 3T. It forms in skarns of Zn deposits and occurs at Franklin Furnace, New Jersey, U.S.A.



henrymeyerite see hollandite



heterophyllite an obsolete varietal term for biotite



hexagonal mica a poorly defined material, possibly a mica



hisingerite Hisingerite is a natural ferric kaolin, analogous to halloysite, that forms partly spherical to spherical morphologies approximately 60-200 in diameter.



hollandite Hollandite (Post et al., 1982) is a manganese oxide mineral within the hollandite supergroup (Biagioni et al., 2012) with a general chemical composition of A0-2B8(O,OH)16, where A = Ba2+ and B = (Mn4+6Mn3+2) in hollandite. The B cations form edge sharing double chains of B-O octahedra, with each double chain forming a wall of a four-sided tunnel. The large A cations, in ideally eight-coordinated sites, reside in the tunnel and offset any undersaturated charge on the octahedra. The supergroup is divided further into the coronadite group (Mn4+ dominates the B cations and includes hollandite) and the priderite group (Ti4+ dominates).

Other minerals in the coronadite group include (A cations) K+ in cryptomelane [ideally B = (Mn4+7Mn3+)], Sr2+ in strontiomelane [ideally Sr(Mn4+6Mn3+2)O16], Pb2+ in coronadite [ideally B = (Mn4+6Mn3+2)], and Na+ in manjiroite [ideally B = (Mn4+7Mn3+)]. Ferrihollandite is BaMn4+6Fe3+2O16. Other B cations in natural samples can include Ti4+, Fe3+, Al3+, Si4+, Mg2+ or additionally, in synthetic phases, Zn2+, In4+, Ni, Cr, and many others. Likewise, A-cation substitutions include Ca, Sr, H2O, vacancies, etc. Priderite is (K,Ba)0-2(Ti4+7Fe3+)8O16 and other members of the priderite group are redledgeite [Ba(Ti4+6Cr3+2)O16], mannardite [Ba(Ti4+6V3+2)O16 . H2O], henrymeyerite [Ba(Ti4+7Fe2+)O16]. The presence or absence of H2O does not define a hollandite-like species. Hollandite-supergroup mineralization occurs in oxidized zones of manganese ores, in hydrothermal deposits, and in some soils. The tunnel topology allows for these minerals to be good ionic conductors for batteries.



holmesite an obsolete term for clintonite



holmite an obsolete term for clintonite



honessite see hydrotalcite group



hormite a term used in industry referring to palygorskite and/or sepiolite. This term should not be used in the scientific literature.



hullite a poorly defined material, found as infillings in cavities in basic igneous rocks, possibly an altered chlorite or a chlorite + smectite mixture



hyalite see opal



hydrobiotite a regular interstratification of biotite-like layers with vermiculite-like layers. The ratio of vermiculite-like layers (i.e., one 2:1 layer and one interlayer capable of limited swelling) to biotite (i.e., one 2:1 layer) is 1:1 (Brindley et al., 1983).



hydrohausmannite a discredited term for a mixture of hausmannite and feitknechtite (beta-MnOOH)



hydrohonessite see hydrotalcite group



hydromicas an obsolete term for interlayer-deficient micas



hydromuscovite an obsolete term for illite



hydroparagonite an obsolete term for brammallite

hydrophlogopite a poorly defined material, possibly interstratified phlogopite and vermiculite



hydropolylithionite a poorly defined material, possibly altered lepidolite



hydrotalcite see hydrotalcite group



hydrotalcite group Hydrotalcite-like and manasseite-like minerals occur as polytypes in rhombohedral and hexagonal forms, respectively. The general formula is [Mg1-xAlx(OH)2]x+ [(CO3)x/2 . nH2O]x- , where x = 0.25 to 0.33 (Drits et al., 1987). In general, the structure is a brucite-like positively charged layer separated by CO3 anions and H2O as interlayer material, but substitutions are common. The International Mineralogical Association recognizes different species (below), based primarily on chemical differences, although there are many other un-named forms. These minerals occur in saline deposits, pegmatites, and serpentinites. Hydrothermal synthesis is relatively easy, as is anion exchange. Cf., anionic clay (Part A), double metal hydroxides (Part A)

barbertonite Mg6Cr2(OH)16CO3 . 4(H2O)

carrboydite (Ni,Cu)5.90Al4.48(OH)21.69(SO4,CO3)2.78 . 3.67(H2O)

chlormagaluminite (Mg3.55Fe2+0.27Na0.05)(Al1.93Fe3+0.07Ti0.01)(OH)12 . Cl2CO3 . 2(H2O)

coalingite Mg10Fe3+2(OH)24CO3 . 2(H2O); Mg16Fe3+2(OH)36CO3 . 2(H2O)

desautelsite Mg6Mn2(OH)16CO3 . 4(H2O)

honessite [Ni5.55Mg0.10Fe3+2.35(OH)16](SO4)1.18 . nH2O

hydrohonessite [Ni5.43Fe3+2.57(OH)16](SO4)1.286.95H2O . 0.98NiSO4

hydrotalcite Mg6Al2(OH)16CO3 . 4(H2O); Mg4Al2(OH)12SO4 . 3(H2O)

iowaite Mg4.63Fe3+1.32(OH)12Cl1.33 . 1.95(H2O)

manasseite Mg6Al2(OH)16CO3 . 4(H2O); Mg4Al2(OH)12CO3 . 3(H2O)

meixnerite Mg6Al2(OH)16(OH)2 . 4(H2O)

motukoreaite [Mg1.82Mn0.03Zn0.02Al1.12(OH)5.15] . [Na0.07K0.07 (CO3)0.40(SO3)0.41 . 2.7(H2O)]

mountkeithite [(Mg8.15Ni0.85)(Fe3+1.31Cr1.02Al0.65)(OH)24](CO3)1.11(SO4)0.38(Mg1.76Ni0.18)(SO4)1.94(H2O)9.39

pyroaurite Mg6Fe3+2(OH)16CO3 . 4.5(H2O); Mg4Ni2+2Fe3+2(OH)16CO3 . 4(H2O)

reevesite Ni6Fe2+2(OH)16CO3 . 4(H2O)

sjögrenite Mg6Fe3+2(OH)16CO3 . 4.5(H2O)

stichtite Mg6Cr3(OH)16CO3 . 4(H2O); [Mg5.94(Cr1.29Al0.51Fe3+0.25)(OH)15.1][(CO3)1.473.7(H2O)]

takovite Ni6Al2(OH)16CO3OH . 4(H2O); [Ni5Mg0.10Fe3+0.13Al2.81(OH)14.42](CO3)2.27 . 5.4(H2O);

Ni6Al2(OH)16SO4OH . nH2O

wermlandite [Mg3.55(Al0.57Fe3+0.41)2(OH)18](Ca0.6Mg0.4)(SO4)2 . 12(H2O)

woodwardite Cu4Al2(OH)12SO4 . 2-4H2O



hydroxyl-annite an obsolete term for annite



hydroxyl-biotite an obsolete term for biotite

iberite a poorly defined material, possibly altered cordierite and zeolite



illite Illite was a term proposed in 1937 by Grim et al. as a "group" name for the mica-like, clay-size mineral constituents in argillaceous sediments. Bailey et al. (1984) indicated that illite, as a species, must meet the following characteristics: (1) the structure is not expansible, (2) the 2:1 layer is dioctahedral, and (3) there are compositional criteria. Rieder et al. (1998) gave a representative formula and typical ranges as: K0.65Al2.0(Al0.65Si3.35)O10(OH)2 where viR2+/(viR2+ + viR3+) < 0.25 and viAl/(viAl + viFe3+) > 0.6 and this differs from muscovite, a closely related mica with an end-member formula and ranges of KAl2(AlSi3)O10(OH)2 where ivSi: 3.0 - 3.1, viAl: 1.9 - 2.0, K: 0.7 - 1.0 (interlayer cations > 0.85), viR2+/(viR2+ + viR3+) < 0.25, and viAl/(viAl + viFe3+): 0.5 - 1.0. The interlayer deficiency observed in illite is considered an important part of the definition. Rieder et al. defined illite as a "series" name, and series names designate that additional research may be warranted. The clay-size aspects and an occurrence in argillaceous sediments are not considered acceptable criteria to define a mineral. When illite is being referred to as a mineral species, it is advisable to make a clear statement to that effect. Non-pure illite, i.e., material containing an expansible component, is referred to as "illitic".



illite/smectite or illite-smectite a phase or mixture of two phases (the status remains unknown) generally showing a non-regular interstratification of illite-like layers with smectite-like layers. The ratio of smectite-like layers (i.e., one 2:1 layer and one interlayer capable of swelling) to illite-like layers (i.e., one 2:1 layer) may vary. Regularity in stacking may be found at specific ratios of layers (I = illite-like, S=smectite-like), for example, ISISIS… or IIISIIISIIIS…, but these patterns of regularity are not of a sufficient long-range nature to designate a separate species. Commonly abbreviated as "I/S" or "I-S".



imogolite a poorly crystallized (i.e., lacks long-range atomic order) hydrous aluminosilicate of approximate composition of (OH)3Al2O3SiOH, with a natural-samples range of Al2(OH)3(SiO2)1.0-1.2(H2O)2.3-3.0. The Si/Al ratio is near 0.5. The structure consists of nanotubes, often occurring in closest packing arrangements about 2nm in diameter and to several micrometers in length, typically forming bundles 10 to 30 nm across. The morphology makes imogolite potentially useful in industry for contaminant sorption, gas storage, as an oxidation catalyst, and as an electron emitter. Imogolite has a gibbsite-like structure with Si tetrahedra spanning the vacant octahedral sites, and because of the mismatch in size between the vacant site and the tetrahedron, the gibbsite-like sheet rolls. Imogolite forms from weathered volcanic ash, but may also occur in podzolized soils and in pumice. Cf., allophane



indianaite an obsolete, local term for a halloysite from Lawrence County, Indiana, in beds to 3 meters thick; may have been used as a rock name for these beds



innsbruckite a modulated 1:1 layer silicate with a continuous edge-sharing, Mn-rich octahedral sheet, and an interstratified continuous tetrahedral sheet consisting of 8-, 6-, 5-, and 4-member tetrahedral rings that cross link the octahedral sheet (Krüger et al., 2014). The chemical composition is ideally Mn33(Si2O5)14(OH)38. The type locality, near Tyrol, Austria, is located between a serpentinite and chert body, and it appears that the Mn-rich sediments were deposited in deep water and metamorphosed. Cf., bementite, pyrosmalite, varennesite



ionite an obsolete, local term for a kaolin forming crusts in the Ione sandstone, California, USA



iowaite see hydrotalcite group



iron mica an obsolete term for annite, siderophyllite, biotite, and hematite



iron muscovite an invalid name for a hypothetical end member



iron-sericite an obsolete varietal term for ferrian illite



irvingite an obsolete varietal term for lithian muscovite



isinglas an obsolete term for muscovite



ivigtite a poorly defined material, possibly muscovite or sodian ferruginous mica



jadeite a pyroxene with chemical formula of NaAlSi2O6. Jadeite occurs in high-pressure, low temperature metamorphic rocks and is the primary mineral in jade. See pyroxene group for additional details.



jefferisite an obsolete name for altered material, probably vermiculite



jennite see tobermorite and see calcium silicate hydrate (CSH) in Part 1



kalifersite a member of the palygorskite-sepiolite group with a composition of (K,Na)5Fe3+7 (Si20O50) (OH)6 . 12(H2O). The kalifersite shows a regular alternation of structural components of sepiolite and palygorskite Ferraris et al. (1998). See palygorskite-sepiolite group



kaliglimmer an obsolete term for muscovite



kandite a name previously proposed for the kaolin/serpentine group. The name has not been approved for use by any mineralogical nomenclature committee and its use should be discontinued.



kaolin (1) Mineralogically, a group name for Al-rich minerals of layer type 1:1 which are dioctahedral and planar (i.e., not modulated). Species include kaolinite, dickite, nacrite, halloysite (planar). (2) Petrologically, a soft, dispersible, usually white or nearly white claystone composed primarily of minerals of the kaolin group, principally kaolinite. Sometimes described as non-plastic. The mixture often contains a variable proportion of, e.g., mica, quartz. Kaolin is white or nearly white on firing; a porcelain clay or natural (unwashed) china clay; and used in the manufacture of ceramics, refractories, and paper. Type locality: Kao-ling (meaning "high hill"), a hill in Kiangsi province, SE China. See also Part 1 of the Glossary. Syn., kaoline, white clay, bolus alba, Cf., dickite, halloysite, kaolinite, nacrite



kaolinite a member of the kaolin group (1:1 layer, dioctahedral), and polymorphic with dickite and nacrite. The chemical composition is Al2Si2O5(OH)4. In kaolinite, the vacant octahedral site is located in the "B" site in each layer to form a triclinic structure. The "B" and "C" sites would be related by a mirror plane if both sites were occupied identically within the same layer, whereas the "A" site resides on the mirror plane (Bish and Von Dreele, 1989). Kaolinite forms under diagenetic and hydrothermal conditions, and may transform to dickite at higher temperatures. At very high temperatures, kaolinite transforms to "metakaolinite". In early publications, kaolinite was used as the group name, now known as kaolin. Cf., dickite, halloysite, kaolin, nacrite



kaolinite/smectite or kaolinite-smectite a non-regular interstratification of kaolinite-like layers with smectite-like layers. Alternatively, the smectite-like layer may be replaced with other expandable layers (e.g., vermiculite). Found in paleosols. May be abbreviated K/S or K-S, and has been referred to as an "kaolinite/expandable" interstratification, K/E (Hughes et al., 1993).



kellyite a platy serpentine mineral of ideal composition of Mn2Al(Si,Al)O5(OH)4, and thus, the Mn2+ analogue of amesite. Mg and Fe2+ have been found to substitute for Mn and Al. Natural occurrences are rare; the type locality is Bald Knob, North Caroline, USA. Stacking disorder is common but, two-layer (2H2) and six-layer polytypes are known to occur. Cf., amesite, zinalsite



kenyaite see magadiite



kerolite a variety of talc, but with H2O either in the interlayer or associated with the broken bonds at the edges of the particles. As a variety of talc, "kerolite" should not be used as a mineral name in a strict sense. Brindley et al. (1977) reported the composition as Mg3Si4O10(OH)2 . nH2O with n = 0.8 - 1.2. Stacking is turbostratic and particle size is < 5 layers. After weeks under ethylene glycol, kerolite swells slightly, whereas talc does not. Kerolite occurs in weathering profiles (Brindley et al., 1977), in palustrine environments (Pozo and Casas, 1999), and in microbial mats in Hawaiin caves (Léveillé et al., 2002), and may be derived from sepiolite (Stoessell, 1988). Older literature may use the spelling of "Cerolite". Cf., pimelite, talc



kerrite an obsolete term for a local variety name of vermiculite



killinite an obsolete term for illite



kimolite an obsolete term for a kaolin, but probably a mixture, described from Kimolos, Greece. Syn. cimolite, pelikanite (from Kiev, Russia, also obsolete)



kinoshitalite a trioctahedral member of the brittle mica group. The end-member formula is: BaMg3Al2Si2O10(OH)2. Typical site substitutions include: Ba > K; Mn2+, Mn3+, Al, Fe, Ti for Mg; and F for OH. Kinoshitalite forms 1M and, less commonly, 2M1 polytypes. In general, kinoshitalite occurs in metamorphic deposits in amphibolite- to granulite-facies, in marbles and calc-silicate rocks, and in kimberlites (group I) and in volcanic rocks that are K undersaturated. Cf., ferrokinoshitalite



klementite an obsolete term for chamosite (chlorite)



kmaite an obsolete term for celadonite, ferrian celadonite



kotschubeite an obsolete term for a Cr-containing chlorite from the Ural mountains



kryptotile a poorly defined material, probably not a mica



kulkeite a regular interstratification of talc-like layers and trioctahedral (tri,trioctahedral) chlorite in a ratio of 1:1 (Abraham et al., 1980). The ideal formula is Mg8Al(Si7Al)O20(OH)10, although substitutions of NaAl = Si to about Si0.4 are known.



kupletskite see astrophyllite group



labradorite see plagioclase feldspar



lamprophyllite see astrophyllite group



larvikite syenite (an igneous rock) dominated by anorthoclase with iridescent colors



lassallite an obsolete name for a poorly defined material from Haute-Loire, France, possibly palygorskite-sepiolite



laumontite see zeolite



ledikite a poorly defined material, possibly interstratified biotite and vermiculite



lembergite an obsolete varietal term for Fe2+-rich saponite



lennilenapeite Mg analogue of stilpnomelane, see stilpnomelane



lennilite an obsolete name for altered material, probably vermiculite



lepidocrocite see boehmite



lepidolite a series name for trioctahedral micas on or close to the trilithionite-polylithionite join. Also used to describe light-colored micas with a significant amount of lithium. Lepidolite is useful as a field term for micas that have not been completely analyzed compositionally, that are commonly found in pegmatite, that have a pink or whitish color. In general, lepidolite, as distinguished from muscovite, commonly crystallizes as the 1M polytype, whereas muscovite is commonly the 2M1 polytype. Lithium is not a chromophore and does not impart the pink color to lepidolite; the presence of Mn probably imparts the pink color to lepidolite.



lepidomelane an obsolete varietal term for annite, siderophyllite, tetra-ferri-annite, and biotite



lepidomorphite an obsolete term for phengite



leptochlorite an obsolete term for an iron-rich chlorite



lesleyite a poorly defined material, possibly margarite or a mineral mixture



leucophyllite an obsolete term for aluminoceladonite



leuchtenbergite an obsolete term for a near iron-free chlorite from the Ural mountains



leverrierite a poorly defined material, probably not a mica, possibly containing halloysite



lilalite an obsolete term for lepidolite



lilalith an obsolete term for lepidolite



lime see calcium silicate hydrate (CSH) in Part 1



lime mica an obsolete term for margarite



lithia mica an obsolete term for lepidolite, zinnwaldite



lithioneisenglimmer an obsolete term for zinnwaldite



lithionglimmer an obsolete term for lepidolite



lithionit an obsolete term for lepidolite



lithionite an obsolete term for lepidolite



lithionitesilicat an obsolete term for lepidolite



lithiophorite Lithiophorite, LiAl2(Mn4+2Mn3+)O6(OH)6, has a structure that contains alternating sheets of (Al,Li)(OH)6 octahedra and sheets of (Mn3+,Mn4+)O6 octahedra. The Al,Li sheet chemistry has an ideal ratio of Al:Li of 1:2, but may vary with charge balance being maintained by the Mn oxidation state. Sheets are held together by hydrogen bonding. Lithiophorite occurs in oxidized zones of Mn ore deposits, acidic soils, and low-temperature hydrothermal environments. Lithiophorite has been identified in nodules from Hawaiian soils.



lithium muscovite an obsolete term for trilithionite, lithian muscovite



lithium phengite an obsolete varietal term for lithian muscovite



lithomarge an obsolete term for a massive, compact, often impure kaolin



lizardite a platy trioctahedral member of the serpentine group. The ideal, end-member formula is: Mg3Si2O5(OH)4. Typical site substitutions include Al and Fe3+ for Si and Mg. The most common form of lizardite is the 1T polytype (space group P31m), followed by the 2H1 polytype (space group P63cm). Lizardite is the most abundant serpentine and forms from the weathering (hydration) of ultramafic rocks, primarily composed of olivine and pyroxene.



lobanovite see astrophyllite group



loughlinite a member of the palygorskite-sepiolite group with a composition of approximately Na4Mg6 (Si12O30)(OH)4 (OH2)4. See palygorskite-sepiolite group



lucianite a poorly described material originally thought to be a "swelling" talc in old literature, but probably saponite, and now considered as an obsolete term



luogufengite Luogufengite is an Al-bearing iron oxide (epsilon-Fe2O3) polymorph that occurs as a nanomineral with large magnetic coercivity (resistant to be affected by an external magnetic field). The structure is orthorhombic with doubled hexagonal (i.e., ABAC) packing of oxygen atoms. Luogufengite occurs as an oxidation product of Fe-bearing basaltic lava or glass at high temperature, and is associated with maghemite and hematite (Xu et al., 2017). The mineral transforms into hematite (alpha-Fe2O3) when the crystal size reaches ~100 nm or larger (Lee and Xu, 2016). Luogufengite may affect high-remnant magnetization of some igneous and metamorphic rocks.



lussatine see opal



lutécine an obsolete name for opal, see opal



lutécite an obsolete name for opal, see opal



mackensite an obsolete term for an iron-rich chlorite



maconite an obsolete term for a poorly defined material perhaps related to vermiculite



macrolepidolite an obsolete term for lepidolite



magadiite a platy, hydrous alkali silicate of composition approximating Na2O . 14SiO2 . 9H2O with exchange properties, and which forms by precipitation from alkaline lakes rich in carbonate/bicarbonate brines, such as that found at Lake Magadi, Kenya. Suggested formulae include NaSi7O13(OH)3 . 3H2O and NaSi6O12(OH). The latter formula, which differs somewhat from the chemical ratio (due to supposed impurities), is derived from a proposed structure model (Garcés et al., 1988) based on the zeolites in the mordenite group: the model consists of continuous sheets of six-fold SiO4 rings of tetrahedra and adjacent five-fold rings pointing away from the sheet surfaces. Other structure models are possible. Kenyaite, with an approximate formula of NaSi11O20.5(OH)4 . H2O, forms under a similar environment as magadiite and is probably a layer structure also.



magnesia mica an obsolete term for phlogopite



magnesiomargarite an obsolete varietal term for clintonite



magnesium sericite an obsolete varietal term for magnesian illite



mahadevite a poorly defined material, possibly Al-rich biotite



manjiroite see hollandite



manandonite a boron-rich serpentine (Ranorosoa et al., 1989), often confused with a boron-rich chlorite in older literature. Manandonite has an ideal chemical composition of Li2Al4(Si2AlB)O10(OH)8 and occurs in the 2H2 polytype. Manandonite occurs in the Antandrokomby pegmatite, Manadona River, near Antsirabe, Madagascar. Cf., borocookeite, boromuscovite



manasseite see hydrotalcite group



manganarsite see pyrosmalite



manganite see groutite



mangan-muscovite an obsolete term for manganoan muscovite



manganese muscovite an obsolete term for manganoan muscovite



manganese mica an obsolete varietal term for biotite



manganglauconite an obsolete varietal term for glauconite



manganmuscovite an obsolete term for manganoan muscovite



manganophyll an obsolete varietal term for biotite



manganophyllite an obsolete varietal term for biotite



manganosite Manganosite, Mn1-xO, is a wustite-type oxide, isostructural with NaCl occurring in low-temperature hydrothermal environments.



manganphlogopite an obsolete varietal term for manganoan phlogopite



manganpyrosmalite see pyrosmalite



mannardite see hollandite



margarite a dioctahedral member of the brittle mica group. The end-member formula is: CaAl2Al2Si2O10(OH)2. Typical site substitutions include: Ca > Na,K; > Li; ivAl Si; ivAl > Be. Margarite is a rock-forming mineral and occurs in low- and medium-grade metamorphic rocks and at nearly all pressure grades. In addition, margarite commonly occurs as pseudomorphs, indicating retrograde reactions and/or polymetamorphism. Margarite most commonly is a 2M1 polytype and, less often, as 1M and 1Md. Tetrahedral site occupancies alternate with Si and Al around the tetrahedral ring, thereby producing a non-centric structure in space group Cc. Cf., bityite



margarodite an obsolete term for muscovite



marienglas an obsolete term for muscovite



mariposite an obsolete term for chromian phengite and chromian muscovite



marmolite an obsolete varietal term for a thinly foliated form of green-white serpentine



marsjatskite an obsolete term for Mn-bearing glauconite from the Urals



marsyatskite an obsolete term for glauconite



masutomilite a trioctahedral member of the true mica group. The end-member formula is KLiAlMn2+AlSi3O10F2. Typical ranges in composition are: Mn2+ = 1.0 - 0.5, Li = 1.0 - 1.5, Si = 3.0 - 3.5, ivAl = 1.0 - 0.5 (Rieder et al., 1998). Masutomilite occurs as a 1M polytype with octahedral ordering, which reduces the ideal space group of C2/m to the acentric subgroup of C2. Masutomilite occurs in granitic pegmatites rich in Li. Cf., zinnwaldite



maufite a discredited term describing a randomly interstratified Ni-bearing lizardite and clinochlore



mcGillite see pyrosmalite



medmontite discredited name for a copper-rich smectite, now known to be a mixture of chrysocolla and mica



meerschaum an older term for a variety of sepiolite often used to make pipes. Some meerschaum samples may contain amorphous material of similar composition to sepiolite. Cf., sepiolite



meixnerite see hydrotalcite group

melanglimmer a poorly defined material, possibly biotite, stilpnomelane, or cronstedtite



melanolite an obsolete term used for an iron chlorite



meroxene an obsolete varietal term for biotite



metabiotite a poorly defined material, possibly a weathering product of biotite



metahalloysite obsolete term for less hydrated form of halloysite, now halloysite (7 )



metajennite see tobermorite



metasericite an obsolete term for muscovite



Mg-illite-hydromica a poorly defined material, possibly interstratified phlogopite and vermiculite



mica see Part 1 of the Glossary



microcline see alkali feldspar



microlepidolite an obsolete term for lepidolite



miloschite an obsolete term for a Cr-bearing kaolinite



minehillite see reyerite group



minguetite (or minguétite) a poorly defined material, possibly interstratified biotite and vermiculite



minnesotaite a modulated 2:1 layer silicate with a continuous octahedral sheet and a tetrahedral sheet that forms linked hexagonal 6-fold tetrahedral rings along strips along the [010] direction (Guggenheim and Eggleton, 1986). Some of the tetrahedra are partially inverted to form a chain along the [010], and this chain links adjacent 2:1 layers. There are two varieties of minnesotaite that are based on strip widths and chemical composition: a P cell is Mg-rich and is formed where 10 tetrahedra span 9 octahedra along the [010] whereas a C cell, which is Fe-rich, forms with 9 tetrahedra spanning 8 octahedra. The ideal chemical composition for the P cell is (Fe,Mg)30Si40O96(OH)28 and (Fe,Mg)27Si26O86(OH)26 for the C cell. Early workers incorrectly considered minnesotaite as the Fe analogue of talc. Minnesotaite occurs in low grade metamorphic silicate iron formations.



modified chlorite structure a Fe-,Mg-rich chlorite, heat treated in air for one-hour at 550 oC to produce a chlorite-like structure (Guggenheim and Zhan, 1999) with a strong d(001) peak (14 ) and weak or absent higher order 00l peaks. The chlorite-to-modified chlorite reaction allows the identification of mixtures of 7 phases (e.g., kaolin minerals) and Fe-,Mg-rich chlorite after heating samples of clay mixtures that may contain chlorite with moderate to high amounts of Fe by revealing the possible presence of 7 peaks in an oriented clay mineral aggregate.



moganite Moganite, a polymorph of quartz, has lower symmetry than quartz (I2/a) and a triclinic superstructure commonly occurs. The structure was described by Miehe and Graetsch (1992) as comprised of sections of right- and left-handed quartz alternating at the unit cell level to form a framework of corner sharing tetrahedra. The framework has 4-, 6- and 8-fold rings, and there is no open tunnel as found in alpha quartz. The nanoscale alternation follows the Brazil twin law, but because it is periodic at the unit cell level, moganite represents a (metastable) mineral phase. Moganite occurs as intergrowths with (alpha) quartz in chert, quartzine, flint, and chalcedony, thus indicating that these latter varieties are not minerals, but rock names. Any H2O present in moganite is not structurally required.



monrepite an obsolete term for ferrian annite



montdorite a trioctahedral member of the true mica group. The ideal formula is KFe2+1.5Mn2+0.5Mg0.5 0.5Si4O10F2 and this formula does not represent an end-member species. A typical range in composition is: Fe2+ > Mn2+ + Mg (Rieder et al., 1998). Robert and Maury (1979) originally described montdorite-1M from a peralkaline rhyolite of the Mont-Dore massif, France, in space group C2/m.



montmorillonite a dioctahedral member of the smectite group of minerals. A representative formula is: R0.33(Al1.67Mg0.33)Si4O10(OH)2.nH2O. Montmorillonite is Al-rich and capable of cation exchange (the exchangeable cation is depicted as R in the formula, n is a rational number, not necessarily an integer). The origin of the layer charge is in the octahedral sheet. In older literature, montmorillonite was used as a group name, which is replaced by the group name, smectite. See also Part 1 of the Glossary for terms that are obsolete: Wyoming-type, Otay-type, Chambers-type, Tatatila-type, beidellite-type (ideal and non-ideal), and non-ideal montmorillonite. Cf., smectite



mordenite see zeolite



morencite an obsolete term for nontronite from Morenci, Arizona, USA



motukoreaite see hydrotalcite group



mountkeithite see hydrotalcite group



muscovite a dioctahedral member of the true mica group. The end-member formula is KAl2 AlSi3O10(OH)2 (where = vacancy). Typical range in composition is: Si= 3.0 - 3.1, ivAl = 1.9 - 2.0, K = 0.7 - 1.0 (although the interlayer site is defined in true micas as I 0.85), viR2+/(viR2+ + viR3+) < 0.25, viAl/(viAl + viFe3+) = 0.5 - 1.0 (Rieder et al., 1998). Muscovite commonly occurs in the 2M1 polytype, and less commonly in 1M, 3T, 1Md, and 2M2 forms. Muscovite is a common rock forming mineral and occurs in igneous, metamorphic, diagenetic, and weathering environments. Cf., nanpingite, paragonite



Na brittle mica an obsolete term for preiswerkite



Na-eastonite an obsolete term for preiswerkite



nacrite (Thomson) an obsolete term for muscovite



nacrite a member of the kaolin group, which consists of the dioctahedral and aluminous rich 1:1 phyllosilicates. Nacrite has a chemical composition of Al2Si2O5(OH)4. Nacrite is distinguished from the other polymorphs, kaolinite and dickite, by the vacant octahedral site regularly alternating from layer to layer across "B" and "C" sites and by a different stacking sequence of layers (Zheng and Bailey, 1994). The "B" and "C" sites would be related by a mirror plane if both sites were occupied identically within the same layer, whereas the "A" site resides on the mirror plane. Dickite and nacrite have a similar alteration of vacant sites, but kaolinite does not. Nacrite differs from dickite by the different stacking sequence. In nacrite the stacking is similar to the 6R polytype, but the vacancy produces monoclinic symmetry. The choice of axes produces a two-layer, monoclinic structure. Nacrite is considered the high-temperature kaolin form, occurring in hydrothermal and pneumatolytic environments. Cf., dickite, halloysite, kaolin, kaolinite



nafertisite see astrophyllite group



nalivkinite see astrophyllite group



nanpingite a dioctahedral member of the true mica group. The ideal end-member formula is CsAl2 AlSi3O10(OH)2 (where = vacancy) and forms as a 2M2 polytype. Nanpingite is the Cs analogue of muscovite and occurs at one locality, the Nanping pegmatite field, Fujian, China.



natrium illite an obsolete term for brammallite



natro-alumobiotite an obsolete varietal term for biotite and sodian siderophyllite



natro-ferrophlogopite an obsolete varietal term for biotite and sodian phlogopite



natronbiotite an obsolete varietal term for biotite



natronmargarite an obsolete term for calcic paragonite, calcic ephesite



natronphlogopite an obsolete varietal term for sodian phlogopite



nelenite see pyrosmalite



nemalite an obsolete, varietal name for fibrous brucite, possibly brucite intergrown with chrysotile



nemaphyllite a poorly described material, possibly a finely divided mixture of serpentine and a Na-containing phase, from Tyrol, Austria



népouite a Ni-rich, planar serpentine where Ni is greater than 50% of the octahedral substitution (Brindley and Wan, 1975), typically NixMg3-xSi2O5(OH)4. Nepouite forms a series with lizardite, the Mg (platy) end member. Stacking disorder dominates, but specimens may approach monoclinic and orthorhombic stacking sequences. Occurrences are complex, but generally involve weathered ultramafics that produce serpentinites followed by lateritic weathering, as is the case for the Ni deposits of New Caladonia. Syn., nepouite.



nickel-gymnite a discredited term, a mixture of pimelite and Ni-rich serpentine



nickel phlogopite an obsolete varietal term for nickeloan phlogopite



nimesite an obsolete name, see brindleyite



nimite the Ni-rich trioctahedral member of the chlorite group. See chlorite



niobokupletskite see astrophyllite group



niobophyllite see astrophyllite group



nontronite Fe3+-bearing and dioctahedral member of the smectite group of minerals. A representative formula is: R0.33Fe3+2(Si3.67Al0.33)O10(OH)2.nH2O, where R refers to the exchangeable cation, commonly Na, Ca and Mg, and n is a rational number, not necessarily an integer. The layer charge originates by substitution primarily in the tetrahedral sheet. One of the dominant minerals along mid-ocean ridges. Cf., smectite



nordstrandite a polymorph of Al(OH)3 that occurs in bauxites and soils and rarely in dolomitic marls. Nordstrandite is a two-layer, dioctahedral structure of Al octahedra (similar to layers found in gibbsite), but with displacements between the layers. Ideally, adjacent layers are superposed in bayerite, offset in nordstrandite, and reversed in gibbsite, presumably because of strong polarization effects of the OH. Cf., gibbsite, bayerite



norrishite a trioctahedral member of the true mica group. The end-member formula is KLiMn3+2Si4O12. The chemical composition of norrishite is noteworthy because it is Li- and Mn-rich and anhydrous, oxygen-rich, and fluorine-poor content. Norrishite forms as the 1M polytype (space group C2/m), and the octahedral sites show Jahn-Teller distortions (Tyrna and Guggenheim, 1991). Norrishite occurs at the (now-filled) Hoskins manganese mine, near Grenfell, New South Wales, Australia.



nsutite Nsutite was originally described as one in a series of similar manganese oxide phases called "gamma MnO2". Zwicker et al. (1962) showed that the samples they studied have a chemical formula more typical of a hydrous component, e.g., Mn(O,OH)2. S. Turner (1982), in a PhD. thesis (Arizona State University), as described in Post (1999), showed that the samples he studied are comprised of random intergrowths of pyrolusite (MnO2) and ramsdellite (MnO2) or a ramsdellite-like phase and, therefore, classification of nsutite as a mineral is questionable. Samples have numerous structural defects and grains commonly have crystallite boundaries. Large deposits occur near Nsuta, Ghana; it has been noted in marine nodules and as residual oxidation products of Mn-rich carbonates. Cf., vernadite

odinite a Fe+3-rich, green, 1:1 serpentine type clay mineral that is intermediate between dioctahedral and trioctahedral, approximately (Fe3+, Fe2+, Mg, Al, Ti, Mn2+)2.5(Si,Al)2O5(OH)4. Odinite forms primarily as 1M (space group Cm) with lesser amounts of 1T (trigonal or hexagonal) polytypes. Octahedral cation totals range from 2.30 to 2.54 cations per 3.0 sites for samples described. Apparently forms in association with organic material on shallow marine shelves and reef lagoonal areas in tropical latitudes.



oblique mica an obsolete term for muscovite



odenite an obsolete term for biotite



odinit an obsolete term for biotite



odith an obsolete term for biotite



oellacherite an obsolete term for barian muscovite



omphacite a clinopyroxene (space group P2/n or C2/c) with an ideal chemical composition of (Ca,Na)(Mg,Al)Si2O6 and this represents the solid solution between augite and jadeite. Ordering and resulting symmetry occurs between Ca and Na (in M2 sites) coupled with ordering between Mg (+Fe) and Al (in M1 sites). Omphacite commonly occurs in high-pressure, high temperature metamorphic rocks, such as eclogite which forms by subduction of oceanic crust. See pyroxene group for additional details.



oncophyllite an obsolete term for muscovite



oncosine a poorly defined material, possibly muscovite with quartz and/or other phases



onkophyllit an obsolete term for muscovite



onkosin a poorly defined material, possibly muscovite with quartz and/or other phases



onkosine a poorly defined material, possibly with muscovite, quartz and/or other phases



opal Opals are microcrystalline or noncrystalline forms (Graetsch, 1994) of SiO2 or SiO2 . nH2O. The H2O is not structurally required. Opal-C (synonym: lussatine) refers to a form with a disordered cristobalite (C) structure, opal-CT (synonym: lussatite, common opal) refers to disordered cristobalite/tridymite intergrowths (CT), and opal-AG (synonym: precious opal) is comprised of cubic- or hexagonal-stacking of closest-packed silica spheres (amorphous spheres of equal size, ~0.0003 mm), where A = amorphous, G = gel-like. Precious opal exhibits opalescence or play of colors in reflected, white light. Opal-AG (synonym: potch opal) lacks opalescence because of disorder in the stacking of planes of the closest-packed spheres. Opal-AN (synonym: hyalite) occurs as botyroidal masses, where N = network or glass-like forms.

opal, common an obsolete term for opal-CT, see opal



opal, potch see opal

opal, precious see opal



orlovite a trioctahedral member of the true mica group. The end-member, ideal formula is KLi2Ti4+Si4O10(O,F), and orlovite occurs as the 1M polytype. Orlovite is from the Darai-Pioz alkaline massif of the Garmskii district, northern Tajikistan. Ti occurs in two positions in what is normally the M1 site in a mica (the M1 site is typically on a center of symmetry, but in orlovite each of the positions is displaced along the m plane away from the center) separated by 0.432 , indicating short range order where Ti is occupied in one domain in one of these positions and in the other domain by the other (Sokolova et al., 2018). Charge balance to offset the 4+ charge of the Ti cation occurs by the substitution of an oxygen anion for fluorine.



orlymanite see reyerite group



orthoclase see alkali feldspar



orthopyroxene a pyroxene subgroup of Mg-Fe pyroxenes in the enstatite-ferrosilite solid-solution series with orthorhombic (Pbca, Pbcn) symmetry. See pyroxene group for additional details. Cf., enstatite



owenite a poorly defined material, possibly an altered iron-rich chlorite, from near Harper's Ferry, West Virginia, USA



oxykinoshitalite a member of the brittle mica group, with an ideal chemical composition of Ba(Mg2Ti4+)Si2Al2O12. Oxykinoshitalite is the Ti and oxygenian dominant analogue of kinoshitalite. Oxykinoshitalite-1M forms in the C2/m space group with Ti primarily in the M2 site. It occurs in an olivine nephelinite from Fernando de Noronha Island, Pernambuco, Brazil (Kogarko et al., 2005).



pagodite an obsolete term for pyrophyllite or a mixture with dominant pyrophyllite



palygorskite a member of the palygorskite-sepiolite group with a composition of approximately (Mg5-y-zR3+yz) (Si8-xR3+x) O20 (OH)2 (OH2)4 . R2+(x-y+2x)/2 (H2O)4, where R are cations, are vacancies, and x, y, and z are compositional parameters. See palygorskite-sepiolite group



palygorskite-sepiolite group The palygorskite-sepiolite group consists of palygorskite, sepiolite, falcondoite, kalifersite, loughlinite, raite, tuperssuatsiaite, yofortierite, windhoekite, and an un-named species, ~NaCa(Fe2+, Al, Mn)5[Si8O19(OH)](OH)7.5H2O. Palygorskite and yofortierite are dioctahedral and all others are trioctahedral. The palygorskite-sepiolite group has infinitely extending tetrahedral sheets involving 6-fold rings of tetrahedra. Tetrahedral sheets have a continuous basal oxygen-atom plane, but the palygorskite-sepiolite group has apical oxygen atoms pointing in opposing directions within a continuous sheet. Each section of like-pointing tetrahedra form a strip or ribbon pattern, and each ribbon consists of a tetrahedral ring (or two pyroxene-like chains) in palygorskite and 1.5 rings (or three pyroxene-like chains) in sepiolite. In palygorskite and sepiolite, the octahedra, which are linked via edge sharing, form strips that are not continuous sheets. In sepiolite, the octahedral strips are eight octahedra wide, whereas strips that are five octahedra in width occur in palygorskite. The terminal anion at the edges of the octahedral strip involves four OH2 groups per formula unit and are required for charge balance. Because these groups are well bonded to the octahedral metal cation and not isolated, they are not referred to as H2O. Vacant regions, zeolitic H2O, and exchangeable cations may reside in the channels formed at the edges of the octahedral strips in palygorskite and sepiolite. Exchange reactions with organic molecules are possible if the size of the organic cations is appropriate, because steric constraints control what can enter this channel. Larger molecules also may be adsorbed by the structure, but this is probably because of defects. Environments of formation range from low-temperature aqueous solutions to high-temperature hydrothermal (< 350 oC) conditions, and natural solutions tend to be alkali-rich with (Na + K)/Al > 1. See individual species for chemical compositions.



palysepiole a name introduced to replace palygorskite-sepiolite. This name has not been accepted by the International Mineralogical Association (or any nomenclature committee) and therefore should not be used.



paragonite a dioctahedral member of the true mica group. The end-member formula is NaAl2AlSi3O10(OH)2, where = vacancy, and thus paragonite is the Na analogue of muscovite. The typical range in composition is: K < 0.5, Ca 0.11. (Rieder et al., 1998). Paragonite occurs as 2M1, 3T, and 1M polytypes. Paragonite is found in low- and medium-grade metapelites and at variable pressures near those of greenschist and blueschist facies. It commonly occurs with muscovite/phengite and margarite. Cf., muscovite



parsettensite a modulated 2:1 layer silicate with continuous Mn-rich octahedral sheets and 6-fold tetrahedral rings forming islands three rings wide. These islands have inter-island linkages, some of which have inverted tetrahedra, involving 12-fold tetrahedral rings and double four-member rings, which act to link adjacent tetrahedral sheets (Eggleton and Guggenheim, 1994). A structural formula for parsettensite is M7.5(Mn,Mg)49(Si64.5Al7.5)=72O168(OH)50 . nH2O. Parsettensite occurs in (low grade to very low grade) metasedimentary manganese ore deposits in Val d'Err, Oberhalbstein, Graubünden, Switzerland and on surfaces of pegmatite minerals by either hydrothermal or pneumatalytic processes at the Foote mine, Kings Mountain, North Carolina, USA, and in a very low grade metagraywacke and argillite near Otago, New Zealand. Cf., stilpnomelane



partridgeite an obsolete term for the Fe-free variety of bixbyite, alpha-(Fe,Mn)2O3



pattersonite a poorly defined material, possibly interstratified biotite and vermiculite



paucilithionite an obsolete term for trilithionite



pearl-mica an obsolete term for margarite



pecoraite the nickel analogue of chrysotile



pectolite see pyroxenoid group



pelikanite an obsolete term for a kaolin, but probably a mixture, described from Kiev, Russia. Syn. kimolite (from Kimolos, Greece, also obsolete), cimolite



pennantite the Mn-rich trioctahedral member of the chlorite group. See chlorite



pennine an obsolete varietal term for clinochlore



penninite a discredited trioctahedral Mg- and Si-rich chlorite, now referred to as clinochlore. See chlorite



perlite see Part 1 of the Glossary.



perraultite see astrophyllite group

pimelite a kerolite-like phase where Ni > Mg



pinguite an obsolete term for nontronite



perlglimmer an obsolete term for margarite



phengite a series name to describe potassium-rich dioctahedral micas between or close to the muscovite-aluminoceladonite join and the muscovite-celadonite join (i.e., Al,Mg,Fe-containing).



philadelphite a poorly defined material, possibly a decomposition product of biotite and vermiculite



phillipsite see zeolite



phlogopite a trioctahedral member of the true mica group. The end-member formula is KMg3AlSi3O10(OH)2. Fe2+ for Mg substitution is common nearly to the Fe end member (annite). Mn and Ti and minor V and Cu substitution is less common. Octahedral vacancies are more prevalent in Fe-containing phlogopite. Phlogopite is defined as having <50% Fe substitution for Mg along the Mg/Fe join. When Fe and Mg content have not been determined, the series name, biotite, is appropriate. Tetrahedral Al substitution tends to be limited to <1.5 cations per formula unit (Fleet, 2003) and Fe3+ and Ti can occupy the tetrahedral site if there is a deficiency in Si. Phlogopite commonly occurs as the 1M and 1Md polytypes, although the 3T and 2M1 forms are less common.



pholerite an obsolete and poorly defined term describing material from Fins, France, similar to kaolin but with apparently excess H2O



pholidolite a poorly defined material, possibly phlogopite or saponite



picrolite an obsolete varietal term for a fibrous to columnar form of green serpentine, often referring to antigorite. The original locality is from Taberg, Sweden, and this material was shown to be carlosturanite. The material from Bare Hills, Maryland, USA, was called baltimorite and is considered an obsolete term also.



picrophengite an obsolete varietal term for magnesian muscovite



pigeonite a clinopyroxene (monoclinic, C2/c space group) with a chemical composition of (Mg,Fe,Ca)(Mg,Fe)Si2O6 where Ca is between about 5 to 15 mole % of CaSiO3 (wollastonite component). Pigeonite forms where the basaltic melt is relatively quickly cooled in, for example, minor shallow intrusions.



pimelite not a valid mineral species, but is often used to describe Ni-rich, 2:1 layer silicates with additional structural H2O. Cf., kerolite



pinite a poorly defined material, possibly a pseudomorph mostly of mica after cordierite,

nepheline, or scapolite



piotine an obsolete term for saponite



plagioclase feldspar Plagioclase feldspar minerals occur in the solid solution series between albite [Ab: Na(Si3Al)O8] and anorthite [An: Ca(Si2Al2)O8] end-members. Ordering between Al and Si is very sluggish in the plagioclase feldspars and requires a coupled substitution between (Si + Na) and (Al + Ca). The plagioclase feldspar minerals are the most abundant minerals in the earth's crust. Plagioclase mineral names are divided into albite (An0-10), oligoclase (An10-30), andesine (An30-50), labradorite (An50-70), bytownite (An70-90), and anorthite (An90-100), but it is increasingly common to designate molecular percentages (i.e., Or10Ab60An30, where Or = orthoclase and Ab and An are defined above). Labradorite feldspar may show iridescent colors at compositions of An50-60 and with Or2-5 where semi-periodic exsolution lamellae occur with periodicity of ~100 nm to ~300 nm. Labrodorite commonly occurs in gabbroic rocks or anorthosites (plagioclase-dominated rocks) that experienced extremely slow cooling history. Plagioclase feldspars are used in glass making and ceramics, paints, rubber, and plastics, although the alkali feldspars are more commonly used in industry. Cf., alkali feldspar



plombièrite see tobermorite 14



polianite The obsolete term "polianite" was once used to refer to crystalline pyrolusite, which was assumed to be a different species than earthy to "crusty" pyrolusite.



poly-irvingite an obsolete varietal term for lepidolite



polylithionite a trioctahedral member of the true mica group. The end-member formula is KLi2AlSi4O10F2, and polylithionite forms a series with siderophyllite. Polylithionite forms as 1M, 2M2, 3T, and 2M1 polytypes and occurs in granitic pegmatites, including pegmatites at Mont St. Hilaire, Quebec, Canada, and the Kola Peninsula, Russia.



potash mica an obsolete term for muscovite



potash margarite an obsolete varietal term for margarite



pregrattite an obsolete term for paragonite



preiswerkite a trioctahedral member of the true mica group. The end-member formula is NaMg2Al(Al2Si2)O10(OH)2. The first occurrence of preiswerkite is from a metamorphosed basic dike in the Geisspfad ultramafic complex in the Penninic Alps. The 1M, 2M1 and 1Md polytypes have been identified. Cf., aspidolite, eastonite



priderite see hollandite



prochlorite a discredited name for an often iron-rich, but Si-poor chlorite



protoenstatite a high-temperature, orthorhombic (Pbcn) polymorph of enstatite. Protoenstatite has been thought to be unquenchable, and commonly transforms to clinoenstatite at low temperature in experiments. However, natural nanoparticle-size protoenstatite has been reported in gem quality "watermelon" sunstones from Oregon, U.S.A. and are apparently quenchable from high-temperature and high-pressure conditions as nanoparticles (Xu et al., 2017).



protolithionite an obsolete varietal term for zinnwaldite, lithian annite, and lithian siderophyllite



pseudobiotite a poorly defined material, possibly interstratified biotite and vermiculite or

interlayer-deficient biotite



pseudo-lussatine an obsolete name for opal, see opal



pseudophite an obsolete term for a compact, massive chlorite that resembles serpentine



pseudo-quartzine an obsolete name for opal or quartzine



pseudosteatite an obsolete term for poorly defined material, impure halloysite



pseudothuringite an obsolete term for low-Si chlorite



psilomelane an obsolete manganese oxide name, now known as cryptomelane, see hollandite. Also, a term used to describe any massive, gray to black, hard, fine-grained manganese oxide material. Often, the latter material is romanechite. Cf., wad, romanechite



pterolite a poorly defined material, possibly a decomposition product of hornblende consisting

of mica and alkali pyroxene



pycnochlorite a poorly defined material, found as infillings in cavities in basic igneous rocks, possibly an altered chlorite or an iron-rich clinochlore



pycnophyllite an obsolete term for fine-grained muscovite or illite



pyknophyllit an obsolete term for fine-grained muscovite or illite



pyroaurite see hydrotalcite group



pyrochroite Pyrochroite, Mn(OH)2, structurally forms sheets of Mn(OH)6 octahedra and is isostructural with brucite. The structure is hexagonal closest packed. Pyrochroite occurs in low-temperature hydrothermal environments. Cf., brucite



pyrolusite see groutite



pyrophyllite the dioctahedral member of the talc-pyrophyllite group. The ideal composition is Al2Si4O10(OH)2. Pyrophyllite forms as a prominent 1A polytype (where A = anorthic, older literature refers to this polytype as 1Tc) and a less prominent, poorly crystalline 2M polytype. The stacking of 2:1 layers in pyrophyllite (Lee and Guggenheim, 1981) is not constrained by an interlayer cation as in the micas, but is related to Si4+ to Si4+ repulsions across the vacant interlayer region. Thus Si tetrahedra between adjacent layers are shifted by ~a/3 so that there are no six-fold or twelve-fold interlayer sites available for interlayer cations, as in mica. Ferripyrophyllite is the ferric iron analogue of pyrophyllite. Pyrophyllite occurs in highly Al-rich metapelites, including metabauxites and metaquartzites, and under hydrothermal conditions. Cf., talc



pyrosclerite an obsolete name for altered material, probably vermiculite



pyrosmalite a modulated 1:1 layer silicate with a continuous, planar octahedral sheet and a general chemical composition of M2+8T6O15(OH,Cl)10. Pyrosmalite is the M = Mn, Fe series, manganpyrosmalite is M for Mn > Fe, and ferropyrosmalite is M for Fe > Mn. Friedelite is the Mn end member and a disordered (polytypic) equivalent of mcGillite. In addition, mcGillite has several additional polytypes. The pyrosmalite structure has an equal number of tetrahedra coordinating to two adjacent octahedra sheets via tetrahedral apical oxygen atoms (Kato and Takéuchi, 1983). Each tetrahedral sheet is composed of 4-, 6-, and 12-fold tetrahedral rings linked laterally, with half of the tetrahedra in the 4- and 12-fold rings inverted. Schallerite and nelenite are polymorphs and similar to friedelite, but apparently with As3O6 molecules within the 12-fold rings. Arsenite analogues of pyrosmalite-type minerals (T = As) occur: manganarsite (analogue manganpyrosmalite), and unnamed arsenite equivalents of schallerite and friedelite. Phase assemblages and occurrences are complex. Pyrosmalite occurs in greenschist facies manganiferous rocks. A near Fe-rich end member was reported from low-grade Fe- and Mn-rich sulfide deposits near Mt. Isa, Queensland, Australia. Friedelite occurs in low-grade metamorphic rocks and is Cl bearing.



pyroxene group The pyroxene group minerals are single-chain silicates with repeat units of two SiO4 tetrahedra (~ 5.2Å) along the chain direction (c-axis). Chemical formulae, using site nomenclature, are given by: M2M1T2O6, where M2 represents medium- to large-size cations, commonly Ca2+, Na+, Fe2+, Mg2+, Mn2+, and Li+; M1 represents small- to medium-size cations like Fe2+, Mg2+, Al3+, Fe3+, and Ti4+; and T represents Si4+ and Al3+ in tetrahedral sites. The minerals develop good {110} cleavage, with cleavage angles near 90 degrees. The pyroxene group is divided further to subgroups according to composition (and symmetry). The common pyroxenes form solid solutions of the Ca-Mg-Fe pyroxenes and are compositionally described (e.g., Morimoto et al., 1988) in the pyroxene quadrilateral with end-members diopside (Di: CaMgSi2O6), hedenbergite (Hd: CaFeSi2O6), enstatite (En: Mg2Si2O6), and ferrosilite (Fs: Fe2Si2O6). The enstatite-ferrosilite solid solution series forms orthopyroxenes (OPX) with orthorhombic (Pbca) symmetry, whereas, the diopside-hedenbergite solid solution series forms clinopyroxenes (CPX) with monoclinic (C2/c) symmetry. Weathering reactions of pyroxene group minerals often produce clay minerals. Pyroxene end-members are: enstatite Mg2Si2O6 (polymorphs clinoenstatite, orthoenstatite, protoenstatite); ferrosilite Fe2Si2O6; diopside CaMgSi2O6; hedenbergite CaFeSi2O6; jadeite NaAlSi2O6; aegirine NaFeSi2O6; spodumene LiAlSi2O6; pigeonite (Mg,Fe,Ca)(Mg,Fe)Si2O6; augite (Ca,Mg,Fe2+,Fe3+,Ti,Al)2(Si,Al)2O6; omphacite (Ca,Na)(Mg,Al)Si2O6; grossmanite CaTiSiAlO6. Refer to individual end members for further descriptions.



pyroxenoid group single-chain silicate minerals with Si-tetrahedral repeats of 3 (e.g., in wollastonite, CaSiO3), 5 (e.g., in rhodonite, MnSiO3), 7 (e.g., in pyroxmangite, FeSiO3), or 9 (e.g., in ferrosilite III). In contrast, the pyroxene tetrahedral repeat is 2. However, both the pyroxenoids and the pyroxenes have octahedrally coordinated cations connecting to the tetrahedral chains in similar ways. Hydrous pyroxenoids exist also, where Na + H substitute for one of the divalent cations, e.g., pectolite, Ca2NaH(SiO3)3. Wollastonite occurs as a contact metamorphic mineral of siliceous dolomites and is used in the manufacture of tile and in glazes. Rhodonite and pyroxmangite occur in manganese deposits and metamorphosed Mn-rich iron formations. Pectolite, commonly associated with zeolites, forms in cavities in basalts as a secondary mineral formed by hydrothermal activity.



pyroxmangite see pyroxenoid group



quartz Quartz, SiO2, is comprised of two chains, both spirals of SiO4 tetrahedra parallel to the c axis. In the alpha-quartz structure (low temperature form to 573 oC at 1 bar), these chains are kinked and the structure has trigonal symmetry. In the beta-quartz structure (high temperature form, above 574.3 oC), the chains expand (the tetrahedra are not twisted) and the symmetry is hexagonal with a more open structure than the alpha form. The beta form is non-quenchable and not found under ambient conditions. An intermediate phase between 573 - 574.3 oC is known to exist. Quartz is a common associated phase in clay, but generally forms grains larger than clay particles (about 0.2 - 0.4 micrometers) and therefore quartz particles can be removed by size separation.



quartzine Quartzine is a rock term to describe a mixture of a fibrous [0001] variety of microcrystalline (length slow) quartz and moganite. Cf., chalcedony



rabenglimmer an obsolete term for zinnwaldite



raite a member of the palygorskite-sepiolite group with a composition of approximately Na3Mn3Ti0.25 (Si8O20) (OH)2. 10(H2O). See palygorskite-sepiolite group



ramesdellite see groutite



ranceite see birnessite



rastolyte a poorly defined material, possibly an altered biotite or interlayer-deficient biotite



rectorite a regular interstratification of dioctahedral mica-like layers and dioctahedral smectite-like layers in a ratio of 1:1 (Brown and Weir, 1963). The structure may be described more completely as pairs of dioctahedral 2:1 layers with alternate interlayers that are mica-like and montmorillonite-like. Mica-like layers may be paragonite-like and the smectite-like layers may be beidellitic. The non-swelling mica interlayers contain about 0.85 univalent cations per mica formula unit and the swelling interlayers about 0.35 univalent cations (e.g., Na, K, but divalent Ca is known also) per smectite formula unit (Bailey, 1982). In the older literature, the name "allevardite" has been used (Bailey, 1982), but the term rectorite has priority.



redledgeite see hollandite



reedmergnerite an albite-like mineral with B in the tetrahedral site, Na(Si3B)O8. Cf., alkali feldspar, feldspar, plagioclase feldspar



reevesite see hydrotalcite group



rensselaerite an obsolete, local term for talc pseudomorphic after pyroxene from northern New York state and Canada



retinalite an obsolete term for a resinous, massive, yellow to green serpentine



revdanskite a discredited name of a material that is primarily pimelite



reyerite see reyerite group



reyerite group Reyerite is comprised of a sheet of edge-sharing Ca octahedra with adjacent tetrahedral sheets of Si8O20 and a double tetrahedral sheet of Si14Al2O38, and an overall chemical composition of (Na,K)2Ca14Si22Al2O58(OH)8 . 6H2O (Merlino, 1988a). The tetrahedral sheets are formed from 6-fold rings of tetrahedra with some tetrahedra pointing up and some down. Na, K, and H2O occupy partially filled sites within the double tetrahedral sheet network. Truscottite, Ca14(Si24O58)(OH)8 . 2H2O, is similar to reyerite, but with alkali and aluminum generally absent, although a limited amount of K and Al can be present and the composition can approach reyerite. Gyrolite, Ca16Si24O60(OH)8 . (14+x)H2O, has a Ca octahedral sheet bounded by Si8O20 tetrahedral sheets as a unit (layer charge may vary from -4 to -5 depending on Al content) separated from other similar units by an interlayer of 2Ca + Na octahedra (Merlino, 1988b). Fedorite, K2(Ca5Na2)Si16O38(OH,F)2 . H2O, has a sheet of edge-sharing Ca octahedra with double tetrahedral sheets, Si16O38, on adjacent sides. Minehillite, (K,Na)2Ca28Zn5Al4Si40O112(OH)16, has a central edge sharing Ca octahedral sheet with a single tetrahedral sheet on one side (similar to reyerite), but a complex slab that differs from reyerite on the other. The structure of cairncrossite, Sr2Ca7-xNa2x(Si4O10)4(OH)2(H2O)15-x, where x is between 0 and 1, forms a unit consisting of edge-sharing Ca octahedral sheets with adjacent Si tetrahedral sheets. These units are cross linked by SrO8 polyhedra. The structure of orlymanite (chemical composition approximately Ca4Mn3Si8O20(OH)6 . 2H2O), which has not been determined, is believed related to reyerite. Synthetic ("K-phase", "Z-phase") phases with structural similarities to reyerite are known. Reyerite group minerals are potentially important in cements used to case geothermal wells where phases form at elevated temperatures and pressures in a steam-rich environment.



rhodonite see pyroxenoid group



rhombenglimmer an obsolete varietal term for phlogopite, biotite



rhombic mica an obsolete varietal term for phlogopite, biotite



ricolite an obsolete varietal term for a banded form of green serpentine



riemannite a discredited name for allophane from Gräfental, Thuringia, Germany



ripidolite a discredited name for an iron-rich, Si-poor chlorite. See chlorite



riversideite see tobermorite



romanechite The structure of romanechite, (Ba,H2O)2(Mn4+,Mn3+)5O10, forms large, rectangular-shaped tunnels bounded by double- and triple-chains of edge sharing MnO6 octahedra. The Mn3+ cations are located in the octahedra at the edges of the triple chains, and the Ba and H2O are located in the tunnels, often in a ratio of 1 to 2. Romanechite occurs in oxidized zones in Mn-rich ore deposits.



roscoelite a dioctahedral member of the true mica group. The end-member formula is KV2AlSi3O10(OH)2. Roscoelite occurs as a 1M polytype and more rarely as 2M1. Roscoelite is found in sedimentary rocks where V has been remobilized from black shales and mafic rocks. Roscoelite is known from the Colorado Plateau district (Colorado, also Utah, Arizona, New Mexico, USA) in U-bearing sandstones. It is also known from Gabon, Western Australia, and Ontario, in the latter occurrence, the V was introduced from metasomatic fluids.



röttisite a discredited name for material primarily containing pimelite



rubellan a poorly defined material, possibly altered biotite or interlayer-deficient

biotite, and/or vermiculite



rumpfite a poorly defined term, possibly for a Si-poor chlorite



saliotite Saliotite is a regular interstratification (mixed layer) of cookeite-like and paragonite-like layers in a ratio of 1:1 (Goffé et al., 1994). The ideal chemical composition is Na0.5Li0.5Al3(Si3Al)O10(OH)5 and it occurs in high-pressure, low-temperature metamorphic rocks (estimated at 280-330 oC, 8 kbar) in Andalusia, Spain. Cf., interstratification



sandbergite an obsolete term for barian muscovite



sanidine see alkali feldspar



saponite Saponite is ideally (M+x-y . nH2O)(Mg3-yR3+y )(Si4-xAlx)O10(OH)2 where M is the exchangeable cation in the interlayer (univalent example given here), R3+ are y trivalent cation substitutions in the octahedral site, x is the number of substitutions for Si by Al in the tetrahedral sites, and n is variable. Natural samples (Moore and Reynolds, 1997) may show < 0.66 Al tetrahedral atoms per asymmetric unit [O10(OH)2] to produce a large negative charge in the tetrahedral sheet which is balanced by positive charge in the octahedral sites (R3+ cations) and interlayer exchangeable (M) cations. Octahedral site vacancies may also occur (Newman and Brown, 1987). Suquet et al. (1975) determined that the two-layer hydrate structure (two planes of H2O) of a Na-saturated sample is C centered with a = 5.333, b = 9.233, c = 15.42 Å, = 96.66 o. The sample approximates a Ia-2 polytype. The d(001) values of saponite commonly range from 13.5 (air dry) to 16.8 (ethylene glycol treatment). Dehydrated K-exchanged saponite shows a mica-like structure with stacking described as either a 1M or 3T structure. Saponite with a Mg-rich octahedral sheet is usually, but not limited to, a weathering product involving volcanic rocks (see Guggenheim, 2011 for a literature review of natural and synthetic saponite). Ferrian saponite (e.g., Kodama et al., 1988) with a composition of (M+0.61 . nH2O) (Mg1.39Fe3+0.85Al0.17Mn0.03) (Si3.49Al0.51) O10(OH)2 and ferrosaponite (Chukanov et al., 2003), (Ca0.31Na0.04K0.01 . 4H2O) (Fe2+1.54Mg0.85Fe3+0.45) = 2.84 (Si2.87Al1.01Fe3+0.12) O9.67(OH)2.33, occur in a gabbro saprolite and as a hydrothermal mineral in basaltic pillow lavas, respectively. Cf., smectite



sarospatakite an obsolete term for illite



sauconite The Zn2+-rich trioctahedral smectite (Ross, 1946) with the ideal composition of (M+x . nH2O)Zn3(Si4-xAlx)O10(OH)2 where M is the exchangeable cation in the interlayer (univalent example given here), x is the number of substitutions for Si by Al in the tetrahedral sites, and n is variable. Zn content may vary commonly from 1.48 to 2.89 atoms per O10(OH)2, and the octahedral site may contain vacancies. Mg, Fe3+, and Al are known to replace Zn (Faust, 1951).



scale stone an obsolete term for lepidolite



schallerite see pyrosmalite



schernikite an obsolete term for muscovite



schrötterite an obsolete term for what is believed to be a mixture of opal and allophane



schuchardite an obsolete term, probably a nickel-bearing chlorite



schuppenstein an obsolete term for lepidolite



seidozerite see astrophyllite group



seladonite an obsolete term for celadonite



sepiolite A member of the palygorskite-sepiolite group with a composition of approximately (Mg8-y-zR3+yz) (Si12-xR3+x) O30 (OH)4 (OH2)4 . R2+(x-y+2z)2 (H2O)8, where R are cations, are vacancies, and x, y, and z are compositional parameters. See palygorskite-sepiolite group



sepiolite-palygorskite group see Part 1 of the Glossary



sericite a poorly defined term, commonly used in the past to describe an optical microscopic fine-grained aggregate of mica-like phases



serpentine see serpentine-kaolin group



serpentine/chlorite (or serpentine-chlorite) a general term used to describe randomly interstratified layers (= "mixed layers") of two types: 1:1 layers (i.e., serpentine-like, 7- spacing) and 2:1 layers + interlayer (i.e., chlorite-like, 14- spacing). The "random" (non-periodic) aspect is important because such a structure will not produce basal X-ray reflections expected by the Bragg equation. A non-periodic structure, i.e., a structure with random interstratifications, is not defined as a mineral (and cannot be given a mineral name). Serpentine-chlorite structures form most commonly under diagenetic conditions as authigenic material associated with pore-linings and fillings, peloids, and replacement phases.



serpentine/kaolin see Part 1 of the Glossary



seybertite an obsolete varietal term for clintonite



shafranovskite a 2:1 hydrous phyllosilicate with continuous sheets of Mn and Na octahedra between two types of tetrahedral sheets. One sheet has isolated Si13(O,OH)37 islands whereas the other has similar islands with SiO3(OH) tetrahedra linkages between islands. The 2:1 layers are apparently not cross linked. The ideal chemical composition is K2Na3(Mn,Fe,Na)4[Si9(O,OH)27] (OH)2 . nH2O, with n ~ 2.33. Shafranovskite occurs in the pegmatites of the Khibiny and Lovozero alkaline complexes, Kola peninsula, Russia.



sheridanite a discredited name for a trioctahedral Mg-rich (Fe-poor), Si-poor chlorite. See chlorite



shilkinite an obsolete varietal term for ferroan muscovite, ferroan illite



shirokshinite a trioctahedral member of the mica group characterized by Na occurring in the octahedral sheet in the M1 site. The ideal chemical composition is K(NaMg2)Si4O10F2. It is found in the apatite mine, Kukisvumchorr Mountain, Khibiny massif, Kola Peninsula, Russia, as a late hydrothermal phase in a small hyperalkaline pegmatite and it forms in the 1M polytype (Pekov et al., 2003).



siderischer-fels-glimmer an obsolete term for lepidolite



siderophyllite a trioctahedral member of the true mica group. The ideal end-member formula is KFe2+2Al(Al2Si2)O10(OH)2, although such a chemical composition has not been reported. The siderophyllite composition is useful to describe solid solution series where there are Fe2+ + Al substitutions, whereas eastonite components involve Mg + Al substitutions. A Tschermak type substitution, which is common in some biotites, involves Aloct + Altet = R2+ + Si. Cf., eastonite



silica Silica refers to the chemistry only, SiO2, and not a specific structure or phase. Cf., silica, amorphous; cristobalite, tridymite, opal



sinopite an obsolete term for an iron-rich red clay used as a pre-history ocher in the Black sea region



sjögrenite see hydrotalcite group



skolite an obsolete term for glauconite



smectite The group name for the 2:1 phyllosilicate minerals with a net negative layer charge between approximately -0.2 and -0.6 per formula unit on the layer. A generalized formula is X0.3Y2-3Z4O10(OH)2 . nH2O, where X is the exchangeable cation (e.g., Ca/2, Na, K, Mg/2), Y is a small to medium size cation (e.g., Al, Cr3+, Fe2+, Fe3+, Li, Mg, Ni, Zn), Z = Si, Al, and n is a rational number, not necessarily an integer). Smectite is often characterized by solvating polar organic molecules into the interlayer causing pronounced swelling between the layers [perpendicular to the (001) plane]. Smectite is commonly referred to as a "swelling clay", as is vermiculite. The rock term, bentonite, refers to a smectite-rich material. See further discussion under Part 1, smectite and obsolete terms: Wyoming-type, Otay-type, Chambers-type, Tatatila-type, beidellite-type (ideal and non-ideal), and non-ideal montmorillonite. Cf., bentonite, swelling clay, beidellite, hectorite, montmorillonite, nontronite, saponite, sauconite, stevensite, swinefordite, volkonskoite, yakhontovite



soda mica an obsolete term for paragonite



soda glauconite an obsolete varietal term for glauconite



soda margarite an obsolete term for calcic paragonite, calcic ephesite



sodium phlogopite an obsolete term for aspidolite



sodium illite an obsolete term for brammallite



spodiophyllite a poorly described material, possibly a mica related to tainiolite



sterlingite an obsolete term for muscovite



stevensite Stevensite is a trioctahedral smectite with an ideal composition of (M+2y . nH2O) (Mg3-y y) Si4O10(OH)2 where M is the exchangeable cation in the interlayer (given here as univalent), represents y vacancies, and n is variable. Stevensite is poorly defined, but the lack of Al, some octahedral vacancies, the high Si content, and the high Mg content are important characteristics. Brindley (1955) described the stevensite structure as two-layer with talc and saponite interstratifications, Faust et al. (1959) suggested that stevensite is a defect structure with two components of talc and talc-like domains, and Shimoda (1971) found stevensite to be composed only of swelling components like smectite minerals. Christidis and Mitsis (2006) studied a Ni-rich stevensite that appeared to confirm the smectite character of one layer type with turbostratic stacking and ethylene glycol intercalation capabilities. Stevensite has been shown to commonly alter from sepiolite, and a Ni-rich stevensite is reported from a supergene alteration of an ophiolite complex in Greece. A significant Al content would allow such a phase to be defined as saponite.



stichtite see hydrotalcite group



stilbite see zeolite



stilpnochlorane an obsolete term, possibly for nontronite or chlorite from Moravia



stilpnomelane a modulated 2:1 layer silicate with a continuous octahedral sheet and a modulated tetrahedral sheet (Eggleton, 1972). The tetrahedral sheet forms approximately hexagonal islands with 6-fold tetrahedral rings and island connectors are formed by an inverted single 6-fold ring with a near trigonal configuration. The islands are comprised of seven near- hexagonal tetrahedral 6-fold rings. The inverted rings also link adjacent layers across the interlayer. Trigonal rings also form by paired trigonal rings joined by the apical oxygen atoms along Z. The primarily ferrous form of stilpnomelane, often informally referred to as "ferrostilpnomelane", has a structural formula of K5Fe2+48(Si63Al9)O168(OH)48 . 12H2O, whereas the analogous "ferristilpnomelane" has a structural formula of K5Fe3+48(Si63Al9)O216 . 36H2O, although neither end-member forms have been found. The Mg-rich stilpnomelane is called lennilenapeite and the Mn-rich mineral is franklinphilite. Older literature incorrectly equates parsettensite as the Mn-rich version. Stilpnomelane occurs in many geological environments, including greenshist facies rocks, iron deposits, metal sulfide deposits, and in weathering profiles.



stolpenite an obsolete local name for a mixture of smectite and a Ca-rich phase(?), or Ca-montmorillonite, from Stolpen, Saxony, Germany



strigovite an obsolete term for an iron-rich chlorite from Striegau, Silesia (now Poland)



strontiomelane see hollandite



sudoite a member of the chlorite group with a composition of Mg2(Al,Fe3+)3(Si3Al)O10(OH)8. The octahedral sheet of the 2:1 layer is dioctahedral, whereas the interlayer is trioctahedral; therefore this is a di,trioctahedral chlorite. It differs from cookeite in that it is essentially Li-free. Cf., chlorite, cookeite, donbassite



suhailite a trioctahedral member of the true mica group with an approximate chemical composition of (NH4, K)(Fe1.33Mg0.71Al0.42Ti0.22)Si2.67Al1.33O10(OH)2. The characterizing feature is the NH4 (NH4 > K) in the interlayer site and the trioctahedral sheet; the composition suggests that suhailite may be described as an ammonium-rich biotite. Difficulties in separating suhailite from impurity phases, stacking disorder and a high numbers of defects prevented structural characterization. Impurity phases and volatility of NH4 limited the accuracy of the chemical analysis. Suhailite occurs in gneisses from the Betic Cordillera, Spain, and formed from primary annite during the annite to fibrolite transformation, probably at temperatures up to ~500 oC (Ruiz Cruz et al., 2009). Cf., tobelite



sveinbergeite see astrophyllite group



svitalskite an obsolete varietal term for celadonite



swelling chlorite see corrensite and chlorite/smectite



swinefordite Swinefordite is the Mg- and Li-rich trioctahedral member of the smectite group, with the original workers (Tien et al., 1975) determining that the location of Li of the natural sample was split with ~33% in the interlayer and the remainder in the octahedral sheet, and with vacancies in the octahedral site, thereby making this a dioctahedral-trioctahedral intermediate. Köster (1982) redetermined the chemistry based on the cation exchange capacity and determined the composition to be (M+0.4 . nH2O)(Li1.06Al0.99 Mg0.7Fe3+0.10)=2.85 (Si3.87Al0.13)O10(OH)2 where M is the exchangeable cation and n is variable. The M (interlayer) cation is assumed here as univalent, but it may have other valence states also. The vacancy content in the octahedral site (0.15) is consistent with other trioctahedral smectites (Güven, 1988). Swinefordite occurs as a pseudomorph after spodumene. Cf., hectorite



taeniolite an obsolete term for tainiolite



tainiolite a trioctahedral member of the true mica group. The end-member formula is KLiMg2Si4O10F2, and tainiolite occurs as 1M, 2M1, and 3T polytypes. Tainiolite is found in alkaline and peralkaline rocks, especially syenites and metasomatites. Syn., taeniolite



takanelite see birnessite



takizolite a poorly described term for material from Yanokami Hill, Omi Province, Japan, possibly a kaolin or smectite



takovite see hydrotalcite group



talc Talc is a 2:1 layer silicate and ideally Mg3Si4O10(OH)2 with layers linked via van der Waals interactions (for a summary, see Evans and Guggenheim, 1988). Layer stacking is controlled by the avoidance of Si to Si electrostatic interactions across the interlayer to form a talc-1A polytype (where A = anorthic, older literature refers to this polytype as 1Tc). There are no six- or twelve-fold sites within the interlayer region as in the micas. The talc-2M polytype is poorly crystalline and rare. Talc is commonly near end-member compositions with more major substitutions of Fe2+ and more minor substitutions of Al and F, with trace substitutions of Mn, Ti, Cr, and Ni. The mineral willemseite is defined for Ni > Mg. Talc occurs in Mg-rich rocks in metamorphosed ultramafic rocks and siliceous dolomites. Talc has also been rarely reported from evaporites, limestones, in beach sands, low-temperature hydrothermal environments, and seafloor sediments. Cf., kerolite, pyrophyllite, willemseite



talcite an obsolete term for muscovite



talc-pyrophyllite see Part 1 of the Glossary



tarasovite originally defined as a regular 3:1 interstratification of (three) dioctahedral mica and (one) smectite layers, but the material is insufficient in regularity to warrant a formal mineral name. The name is in reserve in case a sufficiently regular interstratification of the same type is found.



tetra-ferri-annite a trioctahedral member of the true mica group. The end-member formula is KFe2+3Fe3+Si3O10(OH)2 and the known polytype is 1M. The ferri-iron component is found in the tetrahedral site. Tetra-ferri-annite is commonly associated with stilpnomelane. Stilpnomelane, when coexisting with tetra-ferri-annite, often appears to be replaced by tetra-ferri-annite. Therefore, tetra-ferri-annite occurs in very low-grade metamorphosed iron formations.



tetra-ferriphlogopite a trioctahedral member of the true mica group. The end-member formula is KMg3Fe3+Si3O10(OH)2, and the occurrence of tetra-ferriphlogopite is from Al-poor, ultrabasic magmas under oxidizing (typically late-stage) environments, such as in alkaline-carbonatites and in some mica kimberlites. Tetra-ferriphlogopite occurs as a 1M polytype.



tarbagataite see astrophyllite group



termierite an obsolete term for a clay of unknown composition resembling halloysite, from Haute-Loire, France



thermophyllite an obsolete term for a poorly defined serpentine phase, from Hoponsuo, Finland



thuringite a poorly defined material, found as infillings in cavities in basic igneous rocks, possibly an altered chlorite



titanbiotite an obsolete varietal term for biotite



titanglimmer an obsolete varietal term for biotite



titanmica an obsolete varietal term for biotite



titanobiotite an obsolete varietal term for biotite



tobelite a dioctahedral member of the true mica group. The end-member formula is (NH4)Al2 AlSi3O10(OH)2, where are vacancies. Tobelite-1M (space group C2/m) was first described from Tobe, Japan by Higashi (1982). Single crystal X-ray analysis of tobelite showed the polytype to be 2M2 in space group C2/c (Mesto et al., 2012). Other polytypes (e.g., 2M1, 3T, 2O) are known. Tobelite and most NH4-rich micas form from diagenesis or in low grade metamorphic or hydrothermal environments, although suhailite is believed to occur at much higher temperatures, in gneisses. Cf., suhailite



tobermorite a mineral and mineral group name for a class of hydrated calcium silicate minerals with a strong resemblance to clay minerals, including variability of basal spacing with H2O content, specific surface area, crystallinity, cation exchange (especially with Al substitutions), and polytypism. For example, tobermorite 9 (chemical composition of Ca5Si6O16(OH)2), tobermorite 11 (general formula of Ca4+xSi6O15+2x(OH)2-2x . 5H2O), and tobermorite 14 (Ca5Si6O16(OH)2 . 7H2O; = plombièrite) refer to variations in basal spacings (d(002) values) and different degrees of hydration, which by successive heat treatments ultimately result in progressive dehydration (= "normal" tobermorite) to tobemorite 9. Some tobermorite 14 samples do not dehydrate and are referred to as "anomalous". Clinotobermorite also topotactically dehydrates upon heating to tobermorite 9. Tobermorites have sheets of 7-fold coordinated Ca polyhedra parallel to the (001) and silicate wollastonite-like tetrahedral chains, which link adjacent sheets in tobermoreite 9, forming parallel to the b axis (Merlino et al., 1999). The tetrahedral chains form double-width chains in tobermorite 11 and clinotobermorite, and the double-width chains form zeolitic-type sites for Ca and H2O. Tobermorite is found in hydrothermal altered carbonates (skarns) and basalt vesicles. The tobermorite group is important in cement hydration. Other hydrated calcium silicate phases are also important in cement formation, including an amorphous cement gel (e.g., Ca3SiO5 and cation substituted forms). Other hydrated calcium silicate minerals include jennite (Ca9Si6O18H2(OH)8 . 6H2O) and metajennite, riversideite (?Ca5Si6O16(OH)2), and foshagite (Ca4Si3O9(OH)2). Also see calcium silicate hydrate (CSH) in Part 1



todorokite Todorokite, (Ca,Na,K)0.3-0.5(Mn4+,Mn3+,Mg)6O12 . 3-4.5H2O, is comprised structurally of edge-sharing triple chains of MnO6 octahedra which form tunnels of widths of three octahedra per wall (Post and Bish, 1988). The triple chains are connected by corner sharing. In addition to the 3 by 3 square tunnels, defects are common with tunnel sizes of 3 x 4, with variations to 3 x 9. Octahedra at the edges of the triple chains contain medium size cations, such as Mg or Mn3+, whereas tunnel cations are the larger cations, H2O, and impurity cations. Todorokite occurs commonly in marine nodules, natural coatings, in oxidized portions in Mn ore deposits, and less commonly, in soils.



tosalite an obsolete varietal term for manganoan greenalite (or magnesian caryopilite)



tosudite a regular interstratification of dioctahedral chlorite-like layers and smectite-like layers in a ratio of 1:1. Tosudite must be dioctahedral on average, although tosudite may refer to smectite-like components that are of dioctahedral or trioctahedral character. Dioctahedral chlorite may be of the type di,dioctahedral or di,trioctahedral interstratified with either dioctahedral smectite-like or trioctahedral smectite-like layers. (Bailey, 1982; Frank-Kamenetskii et al., 1965).



tridymite Tridymite, a high temperature polymorph of SiO2, has many structural modifications and these are described by Heaney (1994). Ideally, the basic structure is comprised of sheets of hexagonal tetrahedral rings with alternate tetrahedra around a ring with apices pointing in opposite directions from adjacent tetrahedra. Adjacent tetrahedral sheets are related by a mirror plane to form channels normal to the sheets. Stacking of the sheets follow ABAB... stacking with A representing the initial sheet and B relating to its mirror image. Tridymite rarely occurs upon heating of SiO2 without the presence of a flux. Tridymite occurs as a devitrification phase of obsidian. Cf., cristobalite, quartz



trilithionite a trioctahedral member of the true mica group. The formula is KLi1.5Al1.5AlSi3O10F2. This formula does not represent an end-member composition. Trilithionite occurs in Li-rich, late stage, granitic pegmatites and aplites as 1M, 2M1 and 3T polytypes.



trioctahedral illite a poorly defined material, possibly interstratified biotite and vermiculite



truscottite see reyerite group



tuperssuatsiaite a member of the palygorskite-sepiolite group with a composition of approximately Na1.87Fe2.14Mn0.48Ti0.14 (Si8O20) (OH)2.n(H2O). See palygorskite-sepiolite group



uniaxial mica a poorly defined material, possibly biotite



unghwarit an obsolete term for nontronite or a mixture of nontronite and silica (opal-C?)



vaalite a poorly defined material, possibly vermiculite



varennesite a modulated layer silicate with a continuous Na and Mn octahedra sheet interstratified with a continuous tetrahedral sheet with pairs of 6-fold tetrahedral rings (Grice and Gault, 1995). Each pair of rings is linked to another pair with tetrahedra pointing in opposing direction so that adjacent sheets of octahedra are cross linked. Connecting pairs of tetrahedra are linked such that 4-fold tetrahedral rings and 10-fold rings are formed. The ideal chemical composition is Na8Mn2Si10O25(OH,Cl)2 . 12H2O. The mineral is extremely rare and occurs at the Demix-Varennes Quarry, Quebec, Canada in a peralkaline sill. Cf., bementite, innsbruckite, pyrosmalite

voigtite a poorly defined material, possibly a weathering product of biotite or interlayer-deficient biotite



valuevite an obsolete varietal term for clintonite



vanadinglimmer an obsolete term for roscoelite



vanadium mica an obsolete term for roscoelite



verdite an obsolete term for chromian muscovite



vermiculite Vermiculite refers to a mineral group and an industrial commodity (see part A for a description of both) and a mineral species. As a mineral species, the basic structure is a 2:1 layer [ideally Mg3(Si3Al)O10] regularly interstratified with a partially completed interlayer [Mg0.5(H2O)4], thus with an overall composition of Mg3(Si3Al)O10 . Mg0.5(H2O)4 in either space group Cc or C2/c. Vermiculites are generally alteration products of (trioctahedral) mica or chlorite and form in soils, with most vermiculite species being trioctahedral, although fine-grained soil varieties may be either dioctahedral or trioctahedral. The 2:1 layer has a net layer charge of -0.6 to -0.9 per formula unit, which is offset by the interlayer to achieve overall neutrality. Like smectite minerals, vermiculite has swelling capabilities. Stacking sequences depend on the H2O and cation configurations of the interlayer. See vermiculite and intumescence in Part 1 of the Glossary.



vernadite Vernadite, MnO2 . H2O, is poorly crystalline and not well studied (Post, 1999). It is a mixture of nano-plates of birnessite, buserite, and interstratified birnessite / buserite. Vernadite occurs in the oxidized zone of Mn ore deposits, as buried manganese nodules on the sea floor, and ferromanganese crusts on seamounts. In soils (Chukhrov et al., 1980), vernadite is believed to be related to microbial oxidation of Mn2+.



verona earth an obsolete term for celadonite



veronite an obsolete term for celadonite



viridite an obsolete term for an iron-rich chlorite



viterbite an obsolete term for a mixture of allophane and wavellite from Santa Rosa de Viterbo, Colombia



volkhonskoite see volkonskoite



volkonskoite a dioctahedral member of the smectite group with the dominant octahedral cation of Cr. The layer charge may originate by either tetrahedral or octahedral substitutions. Syn., volkhonskoite



voron'ya slyuda an obsolete varietal term for zinnwaldite, lithian annite, lithian siderophyllite ('Raven mica' or 'crow mica' in Russian).



vredenburgite a discredited term for oriented intergrowths of hausmannite + jacobsite



wad a general term, now obsolete, to describe any poorly defined, fine grained manganese oxide with black or dark brown earthy, dull luster. Cf., psilomelane



waddoite a poorly defined material, possibly a mica



walouewite an obsolete varietal term for clintonite



waluewite an obsolete varietal term for clintonite



walujewit an obsolete varietal term for clintonite



wermlandite see hydrotalcite group



white mica a field term used to describe a light-colored, mica, usually in metamorphic rocks, such as muscovite and margarite, and also illite, phengite, and celadonite



willemseite Willemseite is the Ni-rich (Ni > Mg) member of the talc group. Willemseite occurs at Barberton Mountain Land, Transvaal.



williamsite an obsolete local, varietal term for antigorite serpentine of various colors, but typically green, from West Chester, Chester County, Pennsylvania, USA



windhoekite a member of the palygorskite-sepiolite group with a composition of approximately (Ca1.68Mn0.32)Fe3+2.96(Si7.87 Al0.08)O20(OH)4. 10H1.98O. See palygorskite-sepiolite group



wodanite an obsolete varietal term for biotite



wollastonite see pyroxenoid group



wonesite a trioctahedral mica that shows interlayer deficiency. It is a series name (Rieder et al., 1998) with a generalized composition of Na0.50.5Mg2.5Al0.5(AlSi3)O10(OH)2. The formula indicates that it is not an end-member composition. Series names designate that additional research may be warranted.

woodwardite see hydrotalcite group



wotanite an obsolete varietal term for biotite



xanthophyllite an obsolete varietal term for clintonite



yakhontovite a copper-bearing, approximately dioctahedral, smectite with a chemical composition of Ca0.20K0.01(Fe3+0.83Cu0.84Mg0.67Zn0.02Al0.01)=2.37Si4O10(OH)2. Yakhontovite occurs in highly oxidized sulfide-cassiterite ores at the Pridorozhnoye deposit of the Komsomolsk district, Khabarovskiy Kray, Far-Eastern Region, Russia (Postnikova et al., 1986).



yangzhumingite a member of the true mica group with an ideal composition of KMg2.5Si4O10F2, with possible substitution of 30% Li in the interlayer site. It is characterized by the Mg dominance over Fe, which is characteristic of montdorite. Material suitable for single crystal study has not been found. The type locality is in metamorphosed carbonate rock from Bayan Obo, Inner Mongolia, China (Miyawaki et al., 2011).



yofortierite a member of the palygorskite-sepiolite group with a composition of approximately ~(R2+,R3+,)5 Si8O20(OH, H2O)2(H2O)7, where Mn2+ dominates; R represents a cation and are vacancies. See palygorskite-sepiolite group



zebedassite a poorly defined term, fibrous in habit, possibly a serpentine or chlorite



zeolite In general, zeolite structures are fine grained and are comprised of negatively charged, three dimensional (Si,Al)O4 corner-sharing tetrahedral networks ("framework") which form structural cavities and "extraframework sites". The tetrahedra, with Al substituting Si, have a negative charge that is balanced by exchangeable cations in the extraframework sites. H2O, which is polar, interacts with both the exchangeable cations and the framework, varying in number depending on relative humidity. Hydration and dehydration is generally continuous and reversible, and quite dynamic, although laumontite exhibits non-continuous behavior. Zeolites occur authigenicly, in low-temperature secondary alterations, such as in soils, as hydrothermal alteration products, in altered volcanics, in sediments, and many other environments. See also Part 1 of the Glossary. There are about 75 natural zeolites, and the more common species are given here:

chabazite (Ca0.5,Na,K)4(Al4Si8O24) . 12(H2O)

clinoptilolite (Na,K,Ca0.5)6(Al6Si30O72) . 20(H2O)

erionite K2(Ca0.5,Na)7(Al9Si27O72) . 28(H2O)

laumontite Ca4(Al8Si16O48) . 16(H2O)

mordenite Na3Ca2K(Al8Si40O96) . 28(H2O)

phillipsite K2(Na,Ca0.5)3(Al5Si11O32) . 12(H2O)

stilbite NaCa4(Al9Si27O72) . 30(H2O)



zinalsite a platy serpentine mineral of ideal composition of Zn2Al(Si,Al)O5(OH)4. Zinalsite is the Zn analogue of amesite. Natural occurrences are rare. The type locality is from the oxidation zone of the Akdzhal deposit, Kazakhstan, and it is also known from Sterling Hill, New Jersey, USA. Cf., amesite, kellyite



zinnwaldite a series name for trioctahedral micas on or close to the siderophyllite-polylithionite join. Also used to describe dark micas with significant amounts of lithium.



zircon an orthosilicate (= nesosilicate) mineral Zr(SiO4) that commonly occurs as an accessory mineral in igneous and metamorphic rocks. The mineral may be used for dating the age of its host rock because it contains radioactive U and Th.



zircophyllite see astrophyllite group



zussmanite a modulated trioctahedral 2:1 phyllosilicate with an ideal chemical composition of RM13T18O42(OH)14, with R = Na and K, M = Mg, Mn, Fe2+, Fe3+, Al, and Ti, and T = Si and Al. The structure of zussmanite (Lopes-Vieira and Zussman, 1969) has a continuous octahedral sheet with islands of tetrahedral 6-fold rings on both sites of the octahedral sheet. Each island of 6-fold rings is laterally linked to other islands of six-fold rings by inverted three-fold rings, and these three-fold rings are linked also to the six-fold island tetrahedral rings of the adjacent 2:1 layer. The 6-fold rings align across the interlayer region and form a mica-like interlayer site where the large R cation can reside. Coombsite is the Mn analogue of zussmanite. Zussmanite occurs in blueschist facies metamorphic regimes at the Laytonville Quarry, Mendocino County, California.



zweiaxiger glimmer an obsolete term for muscovite



References for Part 2



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