A trioctahedral member of the true mica group. The end-member formula is KMg₃AlSi₃O₁₀(OH)₂. Fe²⁺ for Mg substitution is common nearly to the Fe end member (annite). Mn and Ti and minor V and Cu substitution is less common. Octahedral vacancies are more prevalent in Fe-containing phlogopite. Phlogopite is defined as having <50% Fe substitution for Mg along the Mg/Fe join. When Fe and Mg content have not been determined, the series name, biotite, is appropriate. Tetrahedral Al substitution tends to be limited to <1.5 cations per formula unit (Fleet, 2003) and Fe³⁺ and Ti can occupy the tetrahedral site if there is a deficiency in Si. Phlogopite commonly occurs as the 1M and 1M_d polytypes, although the 3T and 2M₁ forms are less common.

An obsolete and poorly defined term describing material from Fins, France, similar to kaolin but with apparently excess H₂O.

A poorly defined material, possibly phlogopite or saponite.

The groundwater table in soil or sediment. The phreatic surface is the interface between the vadose zone (unsaturated water content) and the phreatic zone (saturated with water) of a soil/sediment, usually characterized with a zero porewater pressure.

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.