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

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) (Mg_3-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)(Fe_1.33Mg_0.71Al_0.42Ti_0.22)Si_2.67Al_1.33O₁₀(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)(Li_1.06Al_0.99 Mg_0.7Fe³⁺_0.10)_Σ=2.85 (Si_3.87Al_0.13)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 Ca_4+xSi₆O_15+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 KLi_1.5Al_1.5AlSi₃O₁₀F₂. 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 Na_1.87Fe_2.14Mn_0.48Ti_0.14 (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 [Mg_0.5(H₂O)₄], thus with an overall composition of Mg₃(Si₃Al)O₁₀ ^. Mg_0.5(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 (Ca_1.68Mn_0.32)Fe³⁺_2.96(Si_7.87 Al_0.08)O₂₀(OH)₄^. 10H_1.98O. 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 Na_0.5▫_0.5Mg_2.5Al_0.5(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 Ca_0.20K_0.01(Fe³⁺_0.83Cu_0.84Mg_0.67Zn_0.02Al_0.01)_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 KMg_2.5Si₄O₁₀F₂, 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 (Ca_0.5,Na,K)₄(Al₄Si₈O₂₄) ^. 12(H₂O)

clinoptilolite (Na,K,Ca_0.5)₆(Al₆Si₃₀O₇₂) ^. 20(H₂O)

erionite K₂(Ca_0.5,Na)₇(Al₉Si₂₇O₇₂) ^. 28(H₂O)

laumontite Ca₄(Al₈Si₁₆O₄₈) ^. 16(H₂O)

mordenite Na₃Ca₂K(Al₈Si₄₀O₉₆) ^. 28(H₂O)

phillipsite K₂(Na,Ca_0.5)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.