Chert impurities

In the southwestern United States and elsewhere in arid or semiarid climates, rainfall may largely evaporate at the land surface, or it may infiltrate into shallow soil horizons, evaporating there or as it returns toward the surface because of capillary forces. Resultant carbonate mineral layers are called caliche and may occur in and on soils, along with layers of chert (impure, precipitated SiOj) and iron(III) oxides, similarly formed, which are called silcrete and ferricrete. 

A microcrystalline impure form of silica similar to chert. Used for decorative purposes. Rare in industry. 

Chert Cristobalite A mir rocryslalline form of silica. An impure form of flint used in abrasives. A crystalline form of free silica, extremely hard and inert chemically very resistant to heal. Quartz in refractory bricks and amorphous silica in rlialomaceous earth are altered to cristobalite when exposed to high temperatures (calcined). Cristobalite is extensively used in precision casting by the hot wax process, dental laboratory work, and certain speciality ceramics. 

Chert Cristobalite A mk rocrystalline form of silica. An impure form of flint used in abrasives. A crystalline lorn) of free silica, extremely hard and inert chemically very resistant to... 

Chert is defined here, following Folk (1980, p. 79), as a chemically precipitated sedimentary rock, essentially monomineralic and composed chiefly of microcrystalline and/or chalcedonic quartz, with subordinate megaquartz and minor amounts of impurities. Chalcedony, which consists of sheath-like bundles of thin, radiating fibers of SiOi, is rare in most Precambrian chert. Precambrian chert occurs as distinct beds or lenses, particularly in Archean rocks, as nodules or silicified laminae in carbonate rocks, or as a sihceous end-member, as granules or cements in iron formation. 

Chert A cryptocrystalline quartz with sub-microscopic crystal size and impurities that give it color and cloudiness. 

Cherty limestone is an impure form containing substantial levels of chert. It often has poor physical properties. 

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