An obsolete varietal term for biotite.

See pyroxenoid group.

A trioctahedral mica that shows interlayer deficiency. It is a series name (Rieder et al., 1998) with a generalized composition of Na_0.5v_0.5Mg_2.5Al_0.5(AlSi₃)O₁₀(OH)₂, where = vacancy The formula indicates that it is not an end-member composition. Series names designate that additional research may be warranted.

See hydrotalcite group.

An obsolete varietal term for biotite.

The Wulff rule or Gibbs-Curie-Wulff Theorem states that when the surface free energy of a crystal is minimized at equilibrium conditions, the perpendicular distance from a given crystal face to the center of the crystal divided by the surface free energy of that face is a constant for all faces of the crystal.

An obsolete term, see western bentonite.

An obsolete term, see western bentonite.

An obsolete tern, see Western bentonite.

As described by Schultz (1969) based on chemical and thermal analysis, Wyoming-type montmorillonite is a type of montmorillonite characterized by a small net negative layer charge of about -0.35 to -0.85 per O₂₀(OH)₄, with tetrahedral substitutions causing from -0.15 to -0.50 of the total layer charge and specific thermal properties. Current nomenclature for montmorillonite is that it is an Al-rich, dioctahedral smectite with an ideal structural formula of (Al_3.15Mg_0.85)Si₈O₂₀(OH)₄X0.85.nH₂O with layer charge from primarily octahedral substitutions of Mg, whereas beidellite has a net layer charge that occurs from tetrahedral substitutions of Al, with an ideal structural formula of Al_4.0(Si_7.15Al_0.85)O₂₀(OH)₄X_0.85.nH₂O. Although the structure of a mineral is important (not given here), thermal properties are not part of the definition. The Wyoming-type montmorillonite of Schultz (1969) is best described as an intermediate in the montmorillonite-beidellite series. The term ”Wyoming-type montmorillonite” is obsolete and should not be used.