A trioctahedral member of the mica group characterized by Na occurring in the octahedral sheet in the M1 site. The ideal chemical composition is K(NaMg₂)Si₄O₁₀F₂. It is found in the apatite mine, Kukisvumchorr Mountain, Khibiny massif, Kola Peninsula, Russia, as a late hydrothermal phase in a small hyperalkaline pegmatite and it forms in the 1M polytype (Pekov et al., 2003).

A ceramics industry term describing the reduction in size of a solid body relating to dehydration during initial drying and/or devolatilization during the final firing stage of making the ceramic body (e.g., bricks, whiteware, sanitary articles, porcelain, and stoneware).

The shrinkage limit is the boundary water content that separates the semi-solid state of clay from its solid state in the classification of a fine-grained soil. At this water content, further drying of the clay does not cause a change in its total volume (i.e., no shrinkage). However, if the water content is greater than the shrinkage limit, drying causes the clay to shrink. The shrinkage limit is one of the three Atterberg Limits (i.e., liquid, plastic, and shrinkage limits).
Cf., Atterberg Limits

International System (of units); Système International d’Unités.

An obsolete term for lepidolite.

A trioctahedral member of the true mica group. The ideal end-member formula is KFe²⁺₂Al(Al₂Si₂)O₁₀(OH)₂, although such a chemical composition has not been reported. The siderophyllite composition is useful to describe solid solution series where there are Fe²⁺ + Al substitutions, whereas eastonite components involve Mg + Al substitutions. A Tschermak type substitution, which is common in some biotites, involves Al_oct + Al_tet = R²⁺ + Si.
Cf., eastonite

A class of reagents characterized by a central silicon atom coordinated tetrahedrally to four R groups. Such compounds are commonly used to bond an inorganic substrate, such as clay minerals, to a polymer. In the most reactive form, two or three of the R groups are chlorine atoms and the remaining are organic groups. The chlorine atoms in these compounds are very reactive with water and hydrolyze readily to form condensation polymers with Si-O-Si backbones, or the chlorine atoms can react with hydroxyl groups on clay mineral surfaces with loss of HCl. A less reactive form has two or three of the R groups as methoxy or ethoxy groups with the remaining R group being another nonlabile organic group. These silanes can be hydrolyzed to form similar polymers or reactions with hydroxyls on clay minerals, but generally require heat and vacuum to drive the condensation reaction. These agents allow the surface of hydroxyl containing compounds to be converted to hydrophobic or reactive surfaces depending on the character of the organic R group.

A surficial SiOH group, which is able to incorporate or dissociate protons. A ferronol group (FeOH) is an additional surface group that behaves similarly to an aluminol or silanol group.
See aluminol group

Silica refers to SiO₂ chemical composition only and the term does not connote structure. The term commonly is used to describe a mineraloid or a glass, as in a silica-rich glass. Thus, silica does not specifically refer to quartz or opal (but opal has a structure involving small, non- crystalline silica spheres).
Cf., mineraloid

Silica refers to the chemistry only, SiO₂, and not a specific structure or phase.
Cf., amorphous; cristobalite, tridymite, opal