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 The term ”Wyoming-type montmorillonite” is obsolete and should not be used.

The interaction of X-rays (electromagnetic radiation with wavelengths in the approximate range of 0.1 to 10) with matter produces scattering in all directions. The electrons in the matter oscillate to the electric field of the impinging X-rays so that the scatter will be in the same wavelength and frequency of the impinging X-rays. Under certain conditions (defined by the Bragg equation), parallel rays produced by the scatter reinforce each other to produce a diffracted wave, and this is referred to as X-ray diffraction.
Cf., Bragg equation, unit cell

An obsolete varietal term for clintonite.

Substances foreign to a body or an environment, for example, clay in the blood system.

A copper-bearing, approximately dioctahedral, smectite with a chemical composition of Ca_0.20K_0.01(Fe³⁺_0.83Cu_0.84Mg_0.67Zn_0.02Al_0.01)_Σ=2.37Si₄O₁₀(OH)₂. Yakhontovite occurs in highly oxidized sulfide-cassiterite ores at the Pridorozhnoye deposit of the Komsomolsk district, Khabarovskiy Kray, Far-Eastern Region, Russia (Postnikova et al., 1986).

A member of the true mica group with an ideal composition of KMg_2.5Si₄O₁₀F₂, with possible substitution of 30% Li in the interlayer site. It is characterized by the Mg dominance over Fe, which is characteristic of montdorite. Material suitable for single crystal study has not been found. The type locality is in metamorphosed carbonate rock from Bayan Obo, Inner Mongolia, China (Miyawaki et al., 2011).