An invalid term, previously used as a classification of the micas where the number of silicon atoms per formula unit is four per four tetrahedral sites, see Rieder et al. (1998).
Cf., mica, true mica, brittle mica, interlayer-deficient mica, group names

The recording of the change in temperature and/or mass of a material when heated.

Rate of heat flow through a material. Heat flow is given as a unit of cross sectional area, per unit of temperature and time along the direction of heat flow.

The change in volume of a material with increase in temperature. It is often expressed as the coefficient of thermal expansion, which is the degree of expansion divided by the change in temperature.

A clay treated by heating (to dehydroxylation temperatures) to increase reactivity (e.g., as a preparation step to form geopolymers). During thermal activation, the clay minerals (partly) dehydroxylate resulting in distorted structures with broken bonds, which increases reactivity.
Syn., metaclay.
Cf., activated clay, firing

The study of energy (potential, kinetic and internal energy) and its conversion to heat (involving work, determining forces, energy transfer, etc.) to characterize systems. Chemical thermodynamics considers energy changes that occur from reactants to reaction products or with physical changes of state during a chemical reaction. Thermodynamics considers macroscopic qualities (temperature, pressure, volume, composition, etc.) and does not provide mechanistic (atomic theory, atomic structure, molecules, etc.) understanding.

An obsolete term for a poorly defined serpentine phase, from Hoponsuo, Finland.

Material, such as a sliced piece of mineral material, rock material, or soil material, that is mounted on a glass microscope slide, and placed in the optical path of a polarizing (petrographic) microscope is referred to as a “thin section”. The standard thickness of the material mounted on the glass is 30 μm.
See petrographic microscope.

A unique time-dependent process where a material (usually a colloid, gel, dispersion, suspension, soft clay) under conditions of constant volume, composition, and temperature becomes stiffer and stronger with time without external physical, chemical, or mechanical disturbance/input. It is generally believed that the change in certain physico-chemical intermolecular and/or interparticle forces as well as microstructure (e.g., particle contacts, reorientation, and aggregation in a clay suspension) contributes primarily to the thixotropic hardening. Such thixotropic ageing or hardening process usually occurs in a material that has been subjected to remolding or mechanical disturbance. A thixotropically aged material can soften or liquify again upon re-remolding and even undergoes cycles of stiffening and softening upon resting and remolding, respectively, without involving the change in composition, temperature, or volume.

a) In the classic sense, thixotropy refers to a material that exhibits reversible sol-gel-sol-… behavior. For example, ‘chemically modified’ bentonite drilling muds used by the petroleum industry are thixotropic. The property prevents the granular material (“cuttings”) produced during drilling from settling out when drilling is stopped (briefly, or for substantial periods), thus preventing the drill rod from seizing.

b) The ‘modern viscometric’ meaning refers to the increase in shear resistance when the shear rate is increased, and the decrease when the shear rate is reduced. Most thoroughly dispersed clay materials above some relatively low concentration exhibit this phenomenon.
Cf., dilatancy, Newtonian fluid, quick clay, rheopexy