Stishovite

Hand Specimen identification: Stishovite only exists as tiny grains in rocks near meteorite impact craters.

Chemical Composition : SiO2

Hardness : 7 to 8

Specific Gravity4.3

Cleavage/Fracture : {110}/conchoidal

Luster/Transparency : vitreous/transparent

Color : colorless

Streak : white

Optical Properties : Uniaxial 1+ 2, v = 1.799, e = 1.826, d = 0.027.

Crystallography : Tetragonal, a = 4.18, c = 2.66, Z = 2; space group P42/m21/n2/m; point group 4/m2/m2/m.

Habit : Stishovite has a prismatic habit.

Structure and composition : Stishovite is always nearly pure SiO2. The structure is extremely dense and resembles the structure of ru-tile. Si4+ is in octahedral coordination, in contrast with the other SiO2 polymorphs.

Occurrence and associations : Stishovite, a rare, high-pressure polymorph of SiO2, is known only from meteor impact craters.

Varieties :

Related Minerals : SiO2 polymorphs include quartz, cristobalite, tridymite, coesite, and stishovite.

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