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
A poorly defined material, found as infillings in cavities in basic igneous rocks, possibly an altered chlorite.
A glazed or unglazed ceramic plate made by firing milled clay (e.g. kaolin) and quartz, plus added feldspar, carbonates, and/or fluorite. Tiles are commonly used in roofing, walls, floors, mosaics, and art.
Cf., ceramic, glaze, earthenware, stoneware, kaolin
An obsolete varietal term for biotite.
An obsolete varietal term for biotite.
An obsolete varietal term for biotite.
An obsolete varietal term for biotite.
A dioctahedral member of the true mica group. The end-member formula is (NH4)Al2 vAlSi3O10(OH)2, where v are vacancies. Tobelite-1M (space group C2/m) was first described from Tobe, Japan by Higashi (1982). Single crystal X-ray analysis of tobelite showed the polytype to be 2M2 in space group C2/c (Mesto et al., 2012). Other polytypes (e.g., 2M1, 3T, 2O) are known. Tobelite and most NH4-rich micas form from diagenesis or in low grade metamorphic or hydrothermal environments, although suhailite is believed to occur at much higher temperatures, in gneisses.
Cf., suhailite