Van der Waals forces are residual forces between atomic groups or molecules and are comprised of primarily dispersion and dipole-dipole forces. Dispersion forces, or London forces, involve the temporary formation of polarity where one side of an atom (or molecule) may have more electrons at a given moment than the opposing side. Thus, one side is slightly more negative than the other slightly more positive side (by having a deficiency in electrons). Neighboring atoms have similar polarity, and a weak bond is formed where opposite charges between atoms attract each other.

An obsolete term for roscoelite.

An obsolete term for roscoelite.

A modulated layer silicate with a continuous Na and Mn octahedra sheet interstratified with a continuous tetrahedral sheet with pairs of 6-fold tetrahedral rings (Grice and Gault, 1995). Each pair of rings is linked to another pair with tetrahedra pointing in opposing direction so that adjacent sheets of octahedra are cross linked. Connecting pairs of tetrahedra are linked such that 4-fold tetrahedral rings and 10-fold rings are formed. The ideal chemical composition is Na₈Mn₂Si₁₀O₂₅(OH,Cl)₂ ^. 12H₂O. The mineral is extremely rare and occurs at the Demix-Varennes Quarry, Quebec, Canada in a peralkaline sill.
Cf., bementite, innsbruckite, pyrosmalite

Describes a solid solution series where there is a linear relationship between the lattice parameters and the chemical composition (as atomic percentage). The term “law” is a misnomer because a linear relationship often does not exist.

An obsolete term for chromian muscovite.

a) A group name for platy phyllosilicates of 2:1 layer and a layer charge of ~ -0.6 to -0.9 per formula unit. Generally for natural samples, the d(001) value is approximately 14.4-15.6 Å, although other spacings may occur depending on H₂O retention and interlayer occupancy. The group is further divided into subgroups that are either trioctahedral or dioctahedral and these subgroups are further divided into mineral species based on chemical composition. Both vermiculites and smectites have swelling capabilities. Distinguished from smectite in that Mg- exchanged vermiculite has d(001) of 14.5 Å after glycerol solvation, whereas smectite has d(001) of 17.7 Å. Vermiculite occurs in soils, and are most common in subtropical and temperate climates.

b) An industrial/commercial commodity obtained from heat-treated naturally-occurring material composed of hydrous phyllosilicates (e.g., vermiculite, hydrobiotite, biotite). This material is heated rapidly to high temperature to cause exfoliation by volume expansion to produce an expanded product of low bulk density. The product involves an intimate mosaic-like intergrowth of dehydrated or partially dehydrated layers and thus is a heterogeneous mixture of phases. The product resembles vermiculite (senso stricto) primarily based on its physical properties, such as density, some adsorptive properties, and chemical composition.
See “group names”, intumescence.
Cf., smectite

Vermiculite refers to a mineral group and an industrial commodity (see part A for a description of both) and a mineral species. As a mineral species, the basic structure is a 2:1 layer [ideally Mg₃(Si₃Al)O₁₀] regularly interstratified with a partially completed interlayer [Mg_0.5(H₂O)₄], thus with an overall composition of Mg₃(Si₃Al)O₁₀ ^. Mg_0.5(H₂O)₄ in either space group Cc or C2/c. Vermiculites are generally alteration products of (trioctahedral) mica or chlorite and form in soils, with most vermiculite species being trioctahedral, although fine-grained soil varieties may be either dioctahedral or trioctahedral. The 2:1 layer has a net layer charge of -0.6 to -0.9 per formula unit, which is offset by the interlayer to achieve overall neutrality. Like smectite minerals, vermiculite has swelling capabilities. Stacking sequences depend on the H₂O and cation configurations of the interlayer.
See intumescence in Part 1 of the Glossary.

Vernadite, MnO₂ ^. H₂O, is poorly crystalline and not well studied (Post, 1999). It is a mixture of nano-plates of birnessite, buserite, and interstratified birnessite / buserite. Vernadite occurs in the oxidized zone of Mn ore deposits, as buried manganese nodules on the sea floor, and ferromanganese crusts on seamounts. In soils (Chukhrov et al., 1980), vernadite is believed to be related to microbial oxidation of Mn²⁺.

An obsolete term for celadonite.