The Clay Minerals Society Glossary of Clay Science, 2018 version Part Clay-Related Materials (Excluding exchanged phases) achlusite

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(Si_32.5Al_7.5)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 [Ba_0.5(Na,K)_0.5]Al₂(Si_2.5Al_1.5O₁₀)(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 K_0.8R³⁺_1.33R²⁺_0.67(Al_0.65Si_3.87)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 (Mn_3.25Mg_1.95Fe³⁺_0.64)(Si_3.75Fe³⁺_0.17Al_0.08)O_10.2(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)(Mg_3-yLi_y)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 A_0-2B₈(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 [Mg_1-xAl_x(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)_5.90Al_4.48(OH)_21.69(SO₄,CO₃)_2.78 ^. 3.67(H₂O)

chlormagaluminite (Mg_3.55Fe²⁺_0.27Na_0.05)(Al_1.93Fe³⁺_0.07Ti_0.01)(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 [Ni_5.55Mg_0.10Fe³⁺_2.35(OH)₁₆](SO₄)_1.18 ^. nH₂O

hydrohonessite [Ni_5.43Fe³⁺_2.57(OH)₁₆](SO₄)_1.286.95H₂O ^. 0.98NiSO₄

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

iowaite Mg_4.63Fe³⁺_1.32(OH)₁₂Cl_1.33 ^. 1.95(H₂O)

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

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

motukoreaite [Mg_1.82Mn_0.03Zn_0.02Al_1.12(OH)_5.15] ^. [Na_0.07K_0.07 (CO₃)_0.40(SO₃)_0.41 ^. 2.7(H₂O)]

mountkeithite [(Mg_8.15Ni_0.85)(Fe³⁺_1.31Cr_1.02Al_0.65)(OH)₂₄](CO₃)_1.11(SO4)_0.38(Mg_1.76Ni_0.18)(SO₄)_1.94 (H₂O)_9.39

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

reevesite Ni₆Fe²⁺₂(OH)₁₆CO₃ ^. 4(H₂O)

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

stichtite Mg₆Cr₃(OH)₁₆CO₃ ^. 4(H₂O); [Mg_5.94(Cr_1.29Al_0.51Fe³⁺_0.25)(OH)_15.1][(CO₃)_1.473.7(H₂O)]

takovite Ni₆Al₂(OH)₁₆CO₃OH ^. 4(H₂O); [Ni₅Mg_0.10Fe³⁺_0.13Al_2.81(OH)_14.42](CO₃)_2.27 ^. 5.4(H₂O);

Ni₆Al₂(OH)₁₆SO₄OH ^. nH₂O

wermlandite [Mg_3.55(Al_0.57Fe³⁺_0.41)₂(OH)₁₈](Ca_0.6Mg_0.4)(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: K_0.65Al_2.0▫(Al_0.65Si_3.35)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 Si_0.4 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 NaSi₁₁O_20.5(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, Mn_1-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 [010] direction (Guggenheim and Eggleton, 1986). Some of the tetrahedra are partially inverted to form a chain along the [010], and this chain links adjacent 2:1 layers. There are two varieties of minnesotaite that are based on strip widths and chemical composition: a P cell is Mg-rich and is formed where 10 tetrahedra span 9 octahedra along the [010] whereas a C cell, which is Fe-rich, forms with 9 tetrahedra spanning 8 octahedra. The ideal chemical composition for the P cell is (Fe,Mg)₃₀Si₄₀O₉₆(OH)₂₈ and (Fe,Mg)₂₇Si₂₆O₈₆(OH)₂₆ for the C cell. Early workers incorrectly considered minnesotaite as the Fe analogue of talc. Minnesotaite occurs in low grade metamorphic silicate iron formations.
modified chlorite structure a Fe-,Mg-rich chlorite, heat treated in air for one-hour at 550 ^oC to produce a chlorite-like structure (Guggenheim and Zhan, 1999) with a strong d(001) peak (14 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⁺_0.5Mg_0.5 ▫_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 Ni_xMg_3-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 (Mg_5-y-zR³⁺_y☐_z) (Si_8-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 M_7.5(Mn,Mg)₄₉(Si_64.5Al_7.5)_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