Tridymite is a high-temperature polymorph of quartz and usually occurs as minute tabular white or colorless pseudo-hexagonal triclinic crystals, or scales, in cavities in acidic volcanic rocks. Tridymite is stable between 870 and 1470 degrees Celsius. It has a Mohs hardness of 6.5 to 7, a specific gravity of 2.28 to 2.33 and refractive indices of nα=1.471 - 1.482 nβ=1.472 - 1.483 nγ=1.474 - 1.488. Image File history File links Mineraly. ... Image File history File links Mineraly. ... In general, a polymorph is something that can exist in several states or forms. ... Quartz is the most abundant mineral in the Earths continental crust. ... In crystallography, the triclinic crystal system is one of the 7 lattice point groups. ... Ignimbrite is a deposit of a pyroclastic flow. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... The refractive index of a material is the factor by which the phase velocity of electromagnetic radiation is slowed relative to vacuum. ...
Tridymite was first described in 1868 and the type location is in Hidalgo, Mexico. The name is from the GreekTridymos for triplet as tridymite commonly occurs as twinned crystal trillings. A twin boundary occurs when two crystals of the same type intergrow, so that only a slight misorientation exists between them. ...
Common in volcanic rocks, cristobalite is a high-temperature polymorph of quartz and tridymite. ... Coesite is a form of silicon dioxide that is formed when very high pressure (2–3 gigapascals) and moderately high temperature (700 °C) are applied to quartz. ... Stishovite is a form of silicon dioxide that is formed at very high pressure (~ 100 kbar) and temperature (> 1200 ° C), so far as is known only in meteorite impact craters and their ejecta. ...
Most tridymite is believed to crystallize as beta tridymite which has an hexagonal symmetry and later as the crystal cools, it easily converts to tridymite.
The conversion from beta tridymite to tridymite is so easy that the beta tridymite's hexagonal crystals are outwardly preserved in their original form.
The presence of tridymite in a rock is helpful to petrologists (rock scientists) in determining the temperature of the rock at the time it crystallized.
TRIDYMITE, a mineral consisting of silicon oxide or silica, SiO 2, but differing from quartz in crystalline form.
Tridymite occurs in the cavities of acid volcanic rocks (rhyolite, trachyte and andesite); the best-known localities are Cerro San Cristobal near Pachuca in Mexico, the Euganean Hills near Padua, and the Siebengebirge on the Rhine.
Probably identical with tridymite is the form of silica known as asmanite, found in the meteorite which fell at Breitenbach,in the Erzgebirge, Bohemia.
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