The Clay Minerals Society Glossary of Clay Science, 2018 version
Part 2. Clay-Related Materials (Excluding exchanged phases)
achlusite a poorly defined material, possibly sodium mica
adamsite an obsolete term for muscovite
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
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
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 Å 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
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 end-member formula is KFe2+3 AlSi3O10(OH)2.
anomite an obsolete term for biotite
antigorite a platy serpentine with lath-like characteristics. Diffraction studies have shown an atomic superstructure arrangement approximately along the  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 . 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.
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 Å) and d(001) values (~10.9 Å, although somewhat variable vs 10.0 Å in 2:1 phyllosilicates). The supergroup divisions are:
Astrophyllite Group, Fe2+ dominant, direct HOH linkage
tarbagataite (K ▫)CaFe2+7Ti2(Si4O12)2O2(OH)5
Kupletskite Group, Mn2+ dominant, direct HOH linkage
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). These include nafertisite [Na,K, ▫)4(Fe2+,Fe3+, ▫)10(Ti2O3Si12O34)(O,OH)6], bafertisite [(Ba2(Fe,Mn)4(Ti2O4Si4O14)(O,OH)2], perraultite [KBaNa2(Mn,Fe2+)8(Ti,Nb)4Si8O32(OH,F,H2O)7], lamprophyllite Na2(Sr,Ti,Na,Fe)4(Ti2O2Si4O14)(O,F)2, seidozerite (Na2(Na,Mn,Ti)4 [(Na,Ti,Zr)2 O2Si4O14]F2), 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).
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-Å spacing instead of the 7-Å 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▫ (i.e., viLi < vi▫ defined as margarite). 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 KAl2▫BSi3O10(OH)2. Cf., borocookeite, manandonite
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 Na0.65Al2▫Al0.65Si3.35O10(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
buldymite a poorly defined material, possibly biotite and vermiculite or interlayer-deficient biotite
bulgakite see astrophyllite group
buserite a synthetic phase, see birnessite
Calgon® see Part 1 of Glossary
Carborundum® see Part 1 of Glossary
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 end-member formula is KFe3+(Mg, Fe2+)▫Si4O10(OH)2. Typical range in composition is: viR2+/(viR2+ + viR3+) ≥ 0.25, viAl/(viAl + viFe3+) < 0.5, Mg/(Mg + viFe2+) > 0.5 (Rieder et al., 1998).
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  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: BaV2▫Al2Si2O10(OH)2. Typical site substitutions primarily occur in the octahedral site by Al, Fe, and/or Mg.
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
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 end-member formula is KCr2▫AlSi3O10(OH,F)2.
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 Å and outer diameters reported at 220-270, >350, and 490 Å (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
clinoptilolite see zeolite
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.
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, alpha-AlO(OH), and isostructural with goethite, alpha-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
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 end-member formula is KMg2Al(Al2Si2)O10(OH)2. The original eastonite occurrence from Easton, Pennsylvania, USA, was shown to be a mixture of phlogopite and lizardite-1T with some “antigorite-like offsets”.
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
ephesite a trioctahedral member of the true mica group. The end-member formula is NaLiAl2(Al2Si2)O10(OH)2.
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
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+y☐z) (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
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
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.
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 Å), 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
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 Å)] are near kaolinite and x ~2 is halloysite (10 Å). Gentle heating of the halloysite (10 Å) phase will produce halloysite (7 Å), and this is a non-reversible reaction. Halloysite (10 Å) 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 Å) 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 Å). 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
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 or equal to 1.5.
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 Å 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)]
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
jefferisite an obsolete name for altered material, probably vermiculite
jennite see tobermorite
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).
Kaopectate® see Part 1 of the Glossary
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.
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
lamprophyllite see astrophyllite group
Laponite® see Part 1 of the Glossary
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 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
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: CaAl2▫Al2Si2O10(OH)2. Typical site substitutions include: Ca > Na,K; ▫ > Li; ivAl ≈ Si; ivAl > Be
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).
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 Å)
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
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  direction (Guggenheim and Eggleton, 1986). Some of the tetrahedra are partially inverted to form a chain along the , 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  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 Å) and weak or absent higher order 00l peaks. The chlorite-to-modified chlorite reaction allows the identification of mixtures of 7 Å 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 7Å 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. 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).
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 end-member formula is CsAl2 ▫AlSi3O10(OH)2.
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.
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
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
orlymanite see reyerite group
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+y☐z) (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 NaAl2▫AlSi3O10(OH)2. Typical range in composition is: K < 0.5, Ca ≤ 0.11. (Rieder et al., 1998)
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)Σ=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
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 has 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.
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
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
plombièrite see tobermorite 14Å
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.
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.
priderite see hollandite
prochlorite a discredited name for an often iron-rich, but Si-poor chlorite
protolithionite an obsolete varietal term for zinnwaldite, lithian annite, and lithian siderophyllite
pseudobiotite a poorly defined material, possibly interstratified biotite and vermiculite or
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.
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  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
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.
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 KV2▫AlSi3O10(OH)2.
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
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, β = 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 Å (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)Σ = 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+y☐z) (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-Å spacing) and 2:1 layers + interlayer (i.e., chlorite-like, 14-Å 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 end-member formula is KFe2+2Al(Al2Si2)O10(OH)2.
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)Σ=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.
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.
tetra-ferriphlogopite a trioctahedral member of the true mica group. The end-member formula is KMg3Fe3+Si3O10(OH)2.
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 9Å (chemical composition of Ca5Si6O16(OH)2), tobermorite 11Å (general formula of Ca4+xSi6O15+2x(OH)2-2x . 5H2O), and tobermorite 14Å (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 9Å. Some tobermorite 14Å samples do not dehydrate and are referred to as “anomalous”. Clinotobermorite also topotactically dehydrates upon heating to tobermorite 9Å. 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 9Å, forming parallel to the b axis (Merlino et al., 1999). The tetrahedral chains form double-width chains in tobermorite 11Å 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).
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.
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 also Part 1 of the Glossary.
vernadite Vernadite, MnO2 . H2O, is poorly crystalline and not well studied (Post, 1999). It is possibly isostructural with (layer-disordered) birnessite. Vernadite occurs in the oxidized zone of Mn ore deposits. 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
wonesite a trioctahedral mica that shows interlayer deficiency. It is a series name (Rieder et al., 1998) with a generalized composition of Na0.5▫0.5Mg2.5Al0.5(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)Σ=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.
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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