Minerals with the same shape characteristics as asbestos.
Cf., aspect ratio, asbestos, asbestosis.

A general commercial term for two fibrous silicate-mineral groups: chrysotile, the fibrous serpentine mineral, and fibrous amphiboles (amosite, crocidolite, anthophyllite, tremolite, and actinolite) and these two groups are considered hazardous by U.S. regulatory agencies (e.g., Occupational Safety and Health Administration, OSHA). Asbestos minerals are incombustible, make excellent thermal and electrical insulators, resist chemical attack, and have high tensile strength. In addition to being fibrous, other characteristics include flexibility and the ability of fibers to be separated (often capable of being woven). The aspect ratio (i.e., length-to-width ratio) is often defined (as stated within Federal Register, June 8, 1992) as at least 20:1 (and often greater than 100:1) by mining or stone companies. Actinolite and tremolite have no commercial value. Amosite (“brown asbestos”) is a variety of grunerite (along the cummingtonite-grunerite join) whereas crocidolite (“blue asbestos”) is a variety of riebeckite. Asbestos minerals have been implicated as pathogenic when inhaled, although the minerals are not equally pathogenic with chrysotile, which is considerably less dangerous than the amphiboles. OSHA (Federal Register, June 8, 1992) considers asbestos fiber dimensions as the best indicator of significant “fiber pathology”. OSHA considers fiber-dimension lengths most pathologically active at greater than 5 micrometers and these fibers generally have aspect ratios of greater than 10:1 with most greater than 20:1.
Cf., aspect ratio, asbestiform, asbestosis

Asbestosis is a disease that results in fibrosis of the lung from the inhalation of asbestiform particles, such as fibrous serpentine (chrysotile) and fibrous amphibole (crocidolite, amosite, anthophyllite, tremolite, actinolite), which can lead to mesothelioma (cancer). The amphiboles have a much greater residence time in the lung than the serpentines, which dissolve more readily at the pH of lung tissue (Hume and Rimstidt, 1992; Werner et al., 1995). See asbestos, asbestiform.
Cf., asbestiform, asbestos, aspect ratio

The aspect ratio is the ratio of the smallest dimension to the longest dimension. For fibers, the aspect ratio is the ratio between the width to the length. NIOSH defines asbestos, for example, with a length:width ratio (also commonly referred to as “aspect ratio”) of predominantly >3:1 fibers. For platy materials, such as clay minerals or polymer/clay nanocomposites, the properties of the composite are strongly impacted by the morphology of the particle. For montmorillonite the aspect ratio (height to diameter of plate) is generally 1:150. In industry, this ratio is commonly expressed simply as an aspect ratio of 150. The aspect ratio of platy and acicular morphologies is one measure of the anisotropy of nanoparticles.

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

An obsolete term for muscovite.

See astrophyllite group.

The general formula (as given by Sokolova and Hawthorne, 2016) for the astrophyllite group minerals is A_2pB_rC₇D₂(T₄O₁₂)₂IX^OD2X^OA4X^PDnW_A2 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; A_2pB_rW_A2 (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, ▫; X^o refers to anions in the O sheet not bonded to T sites, X^OD = oxygen anions in common at the 3M and D vertices; X^OA = OH, F anions at the common vertices of 3M polyhedra; X^PD = F, O, OH, H₂O, ▫, apical anions of D cations at the edges of the HOH block; W_A = H₂O, ▫; and for X^PDn, 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-X^pD-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
astrophyllite K₂NaFe²⁺⁷Ti₂(Si₄O₁₂)₂O₂(OH)₄F
iobophyllite K₂NaFe²⁺⁷(Nb,Ti)(Si₄O₁₂)₂O₂(OH)₄(F,O)
zircophyllite K₂NaFe²⁺⁷Zr₂(Si₄O₁₂)₂O₂(OH)₄F
bulgakite Li₂(Ca,Na)Fe²⁺⁷Ti₂(Si₄O₁₂)₂O₂(OH)₄(F,O)(H₂O)₂
nalivkinite Li₂NaFe²⁺⁷Ti₂(Si₄O₁₂)₂O₂(OH)₄F(H₂O)₂
tarbagataite (K ▫)CaFe²⁺⁷Ti₂(Si₄O₁₂)₂O₂(OH)₅
Kupletskite Group, Mn²⁺ dominant, direct HOH linkage
kupletskite-1A K₂NaMn₇Ti₂(Si₄O₁₂)₂O₂(OH)₄F
kupletskite-2M K₂NaMn₇Ti₂(Si₄O₁₂)₂O₂(OH)₄F
kupletskite-(Cs) Cs₂NaMn₇Ti₂(Si₄O₁₂)₂O₂(OH)₄F
niobokupletskite K₂NaMn₇(Nb,Ti)₂(Si₄O₁₂)₂O₂(OH)₄(O,F)
Devitoite group
devitoite Ba₆Fe²⁺⁷Fe³⁺²(Si₄O₁₂)2(PO4 )2 (CO3 )O2 (OH)4
sveinbergeite (H₂O)₂[Ca(H₂O)](Fe²⁺⁶Fe³⁺)Ti²(Si₄O¹²)₂O₂(OH)₄(OH,H₂O)
lobanovite K₂Na(Fe²⁺⁴Mg₂Na)Ti₂(Si₄O₁₂)₂O₂(OH)₄
HOH blocks are found in other (heterophyllosilicate) titanosilicates, and these minerals have been described by Ferraris and co-workers (e.g., for a partial summary, see Ferraris, 1997,
Sokolova, 2006, Jin et al., 2018). These include:
nafertisite [Na,K, ▫)₄(Fe²⁺,Fe³⁺, ▫)₁₀(Ti₂O₃Si₁₂O₃₄)(O,OH)₆],
bafertisite [(Ba₂(Fe,Mn)₄Ti₂(Si₂O₇)₂O₂(OH)₂F₂,
jinshajiangite (Na,Ca)(Ba,K)Fe₄Ti₂(Si₂O₇)₂O₂(OH)₂F,
perraultite (Na,Ca)(Ba,K)Mn₄Ti₂(Si₂O₇)₂O₂(OH)₂F,
lamprophyllite Na₂(Sr,Ti,Na,Fe)₄(Ti₂O₂Si₄O₁₄)(O,F)₂,
seidozerite Na_1.6Ca_0.275Mn_0.425Ti_0.575Zr_0.925(Si₂O₇)OF,
and many others. The titanosilicates are found in hyperagpaitic (highly peralkaline nepheline syenites) rocks.

The smallest part of a unit cell from which the entire unit cell can be generated by applying all symmetry operators present.

In geotechnical or soils engineering, the at-rest condition refers to a stress state where a soil or clay deposit is subject to three-dimensional (mutually perpendicular) stresses such that the soil/clay body only deforms vertically (i.e., along the z axis) but not laterally (i.e., along x and y axes). The ideal at-rest condition exists in a soil unit beneath a level, infinite-sized ground surface. In engineering practice, sites with level ground surface and the horizontal dimensions much greater than the vertical dimension (e.g., lake bed sediments with a horizontal surface), can be treated as an at-rest condition. For a component of soil or clay at the at-rest condition, the strains in the x and y directions are zero, and hence the vertical strain is the same as the volumetric strain (= change in volume divided by the original volume). Understanding the at-rest condition is essential for the design of structures situated on or in soil or clay.
Syn., K0 condition.