A solid with a degree of order intermediate to the highly ordered arrangement of atoms, molecules, or ions in a “crystalline” solid and the highly disordered arrangement as found in a “gas”. Most glasses are in a metastable state and can be described as a supercooled liquid, which lack a melting point. Rapid cooling from a molten state (e.g., magma, lava) may result in a glass and this commonly depends on the volatile content of the melt. Not all glasses are formed from a melt. Although most opal forms from silica-saturated fluid under near-surface conditions, a rare “non-crystalline opal” (e.g., opal-AN) forms by transport of silica via steam to cold surfaces.

An iron-rich dioctahedral mica that shows K deficiency and limited substitutions of Al in the tetrahedral sites. Glauconite is a series name (Rieder et al., 1998) with a generalized composition of K_0.8R³⁺_1.33R²⁺_0.67(Al_0.65Si_3.87)O₁₀(OH)₂, where ^viR²⁺/(^viR²⁺ + ^viR³⁺) >= 0.15, and ^viAl/(^viAl + ^viFe³⁺) <= 0.5 and shows no compositional overlap with celadonite. Often interstratified with smectite as the mixed-layered mineral glauconite/smectite. When mixed with other minerals or when referring to morphological features, the term “glauconitic” is appropriate. The mode of origin is not a criterion for identification.

A glaze is a vitreous, watertight coating often used to seal porous ceramics, such as earthenware. Glazes are commonly made from clay mixed with a flux to lower the melting temperature, then applied to the green body and fired. Colorants, commonly iron, copper, or cobalt compounds, may be added, especially to color vases or tiles.
Cf., ceramic, earthenware, green body, tile

Symmetry involving reflection across a plane coupled with a translation of a/2, b/2 or c/2 parallel to an axis (a-glide, b-glide, or c-glide, respectively) or between two axes (n-glide with translations of a/2 + b/2, b/2 + c/2, or a/2 + c/2; d-glide or diamond glide with translations of a/4 + b/4, b/4 + c/4, or a/4 + c/4) or between three axes for tetragonal or isometric crystals with a translation component of a/4 + b/4 + c/4.

An obsolete term for illite.

See diaspore.

A poorly known, modulated 2:1 layer silicate (Guggenheim and Eggleton, 1987). Although superficially resembling chlorite, gonyerite has a two-layer structure with structurally different types of interstratified layers. Inverted tetrahedra occur between the 2:1 layer and linked to the what would be the brucite-like interlayer in an ideal chlorite. Samples of gonyerite are generally impure, although an analysis by Frondel (1955) reported an approximate composition of (Mn_3.25Mg_1.95Fe³⁺_0.64)(Si_3.75Fe³⁺_0.17Al_0.08)O_10.2(OH)_7.8 and is based on the assumption that gonyerite is a chlorite and all iron is ferric. Gonyerite occurs in low-grade metamorphic, silicate-rich manganese deposits, such as that at the Harstigen Mine, Pajsberg, Värmland, Sweden.

An obsolete term for nontronite.

A Monte Carlo molecular simulation that is based on the grand canonical thermodynamic ensemble, an ensemble (e.g., a system of particles) in statistical mechanics that describes the possible states of the particles in equilibrium. The model system properties of chemical potential, volume, and temperature are held constant, but the number of particles in the system (e.g., interlayer water molecules) is allowed to vary as equilibrium is achieved. In this context, equilibrium implies both potential energy and system density (number of particles). Monte Carlo moves are accepted based on the energy change of the move according to a Boltzmann probability (so that some moves resulting in higher energy are accepted).
Cf., force field, molecular dynamics, Monte Carlo molecular simulation

See garnet.