Cristobalite
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Cristobalite is a mineral polymorph of silica that is formed at very high temperatures. It has the same chemical formula as quartz, SiO2, but a distinct crystal structure. Both quartz and cristobalite
Cristobalite spherulites formed by devitrification from the obsidian matrix. Specimen from California, US; size: 5.9 cm × 3.8 cm × 3.8 cm (2.3 in × 1.5 in × 1.5 in).
Tridymite
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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 for
Cristobalite
…but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all the members of the quartz group, which also include coesite, tridymite and stishovite. It is named after Cerro San Cristóbal in Pachuca Municipality, Hidalgo, Mexico. It is used in dentistry as a component of alginate…
Tabular tridymite crystals from Ochtendung, Eifel, Germany