Stishovite Mineral Physical and Optical Properties

Origin of Name

Named after S.M. Stishov, an early investigator of high pressure SiO2 polymorphs.

Hand Specimen Identification

Stishovite only exists as tiny grains near meterorite impact craters.

Stishovite

Physical Properties

Hardness	7 to 8
Specific Gravity	4.30
luster/transparency	vitreous/transparent
Color	colourless
streak	white
Fracture	Conchoidal
Cleavage	{110}

Optical Properties

Uniaxial (+), Womega = 1.799, Epsilon = 1.826, Delta = 0.027

3D Structure

Stishovite model showing the tetragonal structure. Note that unlike the other silica polymorphs which are built with SiO4 tetrahedra, in stishovite silicon is coordinated with 6 oxygen anions in an octahedral arrangement. This forms a much denser structure in response to increased pressure.

Crystallography

Tetragonal, a = 4.18, c = 2.66, Z = 2

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Habit

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 rutile. 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.

Related Minerals

SiO2 polymorphs include quartz, cristobalite, tridymite, coesite, and stishovite.