An obsolete name for astrophyllite.

Brucite is a hydroxide mineral with the composition of Mg(OH)₂. Also, brucite has been used as a group name for M²⁺(OH)₂ where M = Fe, Mg, Mn, Ni. Brucite is comprised of a plane of Mg cations, with each Mg octahedrally coordinated by edge-sharing OH groups, thus forming an infinite two-dimensional sheet. Brucite primarily occurs as a contact metmorphic mineral in dolomites and Mg-rich limestones from the alteration of periclase, and in serpentinites and chlorite schists.

Inappropriate usage for trioctahedral sheet.
See trioctahedral sheet, interlayer material

Surface area determination by sorption analysis of non-polar gases, typically N₂, on a solid, as calculated from the linear form of the BET equation (see Brunauer et al., 1938) for multi-layer gas adsorption on the surface of a sample of known weight. The technique requires removal of sorbed gases from the sample prior to BET analysis. Objections involving the use of BET analysis for clays containing H₂O include 1) platy surfaces of the phyllosilicate particles protect underlying adjacent surfaces from gas adsorption, and 2) interlayer regions may become inaccessible to N₂ owing to pretreatments that remove interlayer H₂O, which collapses any swelling clays present, and thus results may be affected by preparation techniques. It is commonly considered to measure external surface area and, as such, should not be used for total specific surface area or as an indicator of the amount of chemically accessible internal surface area.

An obsolete varietal term for manganoan zincian chamosite.
See chlorite

An ammonia-dominated feldspar mineral, NH₄(Si₃Al)O₈.
Cf., alkali feldspar, feldspar, plagioclase feldspar

A poorly defined material, possibly biotite and vermiculite or interlayer-deficient biotite.

See astrophyllite group.

A measure of the resistance of a material to external stress, in units of pressure (usually gigapascals), by fitting the incremental change in potential energy with incremental change in volume (e.g., Birch-Murnaghan equation of state). The bulk modulus is measured by experiments or by simulations and best describes isotropic materials.
Cf., elastic constant.

See unit weight, effective.