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.

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).

A designated series of parameters (i.e., water-content properties) in geotechnical engineering used for identifying, describing, and classifying fine-grained soils and clays or loams used for (ceramic) coarse ware. These parameters, which originally included six “limits of consistency” (the upper limit of viscous flow, the liquid limit, the sticky limit, the cohesion limit, the plastic limit and the shrinkage limit) are now typically limited to the “liquid limit”, the “plastic limit” and, sometimes, the “shrinkage limit”. Atterberg limits are determined on the basis of mass of water per mass of the dry soil solid by specific test methods, as standardized by ASTM Standard D4318 – 05 or other standard tests, and expressed in percent.
See Mitchell (1993).
See also activity, consistency number, liquid limit, plastic limit, plasticity index, shrinkage limit

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

Refers to rock constituents or minerals that have formed in place and were not transported. Such materials have formed either at the same time as the rock in which they are found or after the formation of the rock. The term is also applied to minerals that are clearly the result of new crystal growth on older crystals of the same kind, e.g., K-rich feldspar overgrowths may be referred to as authigenic overgrowths.

In a molecular dynamics simulation, the autocorrelation function is a time-dependent function calculated from the product of a quantity at a given time relative to an initial reference time. Specific autocorrelation functions are used to calculate vibrational spectra. For example, the velocity autocorrelation function is used to determine a power spectrum, and the dipole moment autocorrelation function is used to calculate the infrared spectrum.

A poorly defined material, possibly chromian illite or a mineral mixture.