What is tridymite and cristobalite?
What is tridymite and cristobalite?
Tridymite and cristobalite are high-temperature, low-pressure polymorphs of silica, forming stably above 870 °C (tridymite) and 1470 °C (cristobalite). In addition, they can form metastably in some low-temperature environments (e.g., they often form during the devitrification of siliceous volcanic or synthetic glass).
What is stishovite used for?
THE MINERAL STISHOVITE. Chemistry: SiO2; Silicon Dioxide. Group: Rutile and Quartz. Uses: As an indicator of a meteor impact and as mineral specimens.
Where is stishovite found?
The results are particularly exciting because stishovite is exactly the mineral found in shocked rocks at the Barringer Crater and similar sites across the globe. Indeed, stishovite (named after a Russian high-pressure physics researcher) was first found at the Barringer Crater in 1962.
What type of mineral is stishovite?
silicon dioxide
Stishovite is an extremely hard, dense tetragonal form (polymorph) of silicon dioxide….
| Stishovite | |
|---|---|
| IMA symbol | Sti |
| Strunz classification | 4.DA.40 (Oxides) |
| Crystal system | Tetragonal |
| Crystal class | Ditetragonal dipyramidal (4/mmm) H–M symbol: (4/m 2/m 2>/m) |
What is tridymite formation?
Tridymite is a high-temperature polymorph of silica and usually occurs as minute tabular white or colorless pseudo-hexagonal crystals, or scales, in cavities in felsic volcanic rocks. Its chemical formula is SiO2. Tridymite was first described in 1868 and the type location is in Hidalgo, Mexico.
How is cristobalite formed?
Cristobalite occurs as white octahedra or spherulites in acidic volcanic rocks and in converted diatomaceous deposits in the Monterey Formation of the US state of California and similar areas. Cristobalite is stable only above 1470 °C, but can crystallize and persist metastably at lower temperatures.
How is stishovite formed?
Stishovite was first discovered in sandstone that had been converted to glass at Meteor Crater, Ariz., and its occurrence with coesite in many other craters is evidence that it was formed by kinetic energy imparted by large-scale impact on the surrounding rock.
Is stishovite a mineral polymorph?
Representative Chemicals: Quartz; Cristobalite; Stishovite; Tridymite; Coesite; these various forms of minerals with the same molecular formula are called polymorphs.
Where is tridymite formed?
Tridymite forms thin hexagonal plates that are generally twinned, often in groups of three; its name alludes to this habit. It commonly occurs in igneous rocks, more abundantly than cristobalite, as in the trachytes of Rhineland-Palatinate, Germany; northern Italy; and in the Massif Central, France.
What is tridymite quartz?
Tridymite is a rare polymorph of the mineral Quartz. However, its crystals are very distinct and form very different habits from Quartz. Many Tridymite specimens are in fact pseudomorphs of Quartz after Tridymite, as the Tridymite often alters to the more common Quartz in many environments.
Is silica a cristobalite?
cristobalite, the stable form of silica (silicon dioxide, SiO2) between its melting point of 1,728° C (3,142° F) and 1,470° C (2,678° F), below which tridymite is the stable form.
