A family of minerals contain continuous two-dimensional tetrahedral sheets of composition T₂O₅ (T = Si, Al, Be…) with tetrahedra linked by sharing three corners of each, and with a fourth corner pointing in any direction. The tetrahedral sheets are linked in the unit structure to octahedral sheets, or to groups of coordinated cations, or individual cations. Although continuous tetrahedral sheets often form six-fold rings, other ring configurations are considered part of the phyllosilicate family.
See Guggenheim et al. (2006) and references therein.
Cf., clay mineral

The breakdown of rocks to fragments through primarily non-chemical processes. Non-chemical processes may include, but are not limited to, ice and/or root wedging, thermal expansion, stress release (e.g., exfoliation), and physical consequences of crystal wedging, and volume change caused by hydration and/or dehydration. Physical weathering may be biologically influenced.
See weathering, chemical weathering

A disorder involving the eating of material that does not have nutritional value. Pica is the more general term for the eating of odd things, such as clay, ice, hair, starch, etc.
Cf., geophagy

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.

An obsolete varietal term for magnesian muscovite.

A property of crystals where an electric moment forms in proportion to tension or compression, with a reversal in polarity depending on the direction of the stress. The phenomenon is dependent on certain non-polar crystal classes or symmetries of the material. A “converse piezoelectric” effect is known where the crystal changes shape if an electric current is applied along the polar axis. Quartz exhibits piezoelectric and converse piezoelectric effects.

A clinopyroxene (monoclinic, C2/c space group) with a chemical composition of (Mg,Fe,Ca)(Mg,Fe)Si₂O₆ where Ca is between about 5 to 15 mole % of CaSiO₃ (wollastonite component). Pigeonite forms where the basaltic melt is relatively quickly cooled in, for example, minor shallow intrusions.

A clay mineral intercalated with small organic or inorganic complexes (or “pillars”), which do not completely fill the interlayer space. The size and shape of the resultant cavities (or “galleries”) are determined by the size, shape, and orientation of the pillars. Pillared clays are potentially useful to remove organic molecules based on shape-selective adsorption (“molecular sieves”). For clays, intercalations involve positively charged complexes (either organic or inorganic “cations”) to offset the negatively charged layers of the clay. Common types of complexes include those of the methylammonium group (organic) and the Keggin ion (Al13, inorganic). Other types of layered materials can also be pillared.
See Keggin ion.
Cf., zeolite

A kerolite-like phase where Ni > Mg.

Not a valid mineral species, but is often used to describe Ni-rich, 2:1 layer silicates with additional structural H₂O.
Cf., kerolite