Coesite

Hand Specimen identification: Coesite cannot be identified in hand specimen.

Chemical Composition : SiO2

Hardness : 7 to 8

Specific Gravity2.93

Cleavage/Fracture : none/conchoidal

Luster/Transparency : vitreous/transparent

Color : colorless

Streak : white

Optical Properties : Biaxial 1+ 2, a = 1.59, b = 1.60, g = 1.60,d = 0.01, 2V = 64°.

Crystallography : Monoclinic, a = 7.17, b = 12.33, c = 7.17, b = 120.0°,

Z = 16; space group C2/c; point group 2/m.

Habit : Crystals are usually thin tabs, invisible without a microscope.

Structure and composition : Coesite’s structure consists of a very dense three-dimensional network of SiO4 tetrahedra. In some ways, the structure is similar to that of feldspars.

Occurrence and associations : Coesite, a rare high-pressure polymorph of SiO2, is known only from meteor impact craters and some rare xenoliths and other rocks of deep crust or man-tle origin

Varieties :

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

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