Opal

November 21st, 2008 by

For other uses, see Opal (disambiguation).
Opal

An opal bracelet. The stone size is 18 by 15 mm (0.7 by 0.6 inch).
General
Category
Mineraloid
Chemical formula
Hydrated silica. SiO2·nH2O
Identification
Color
White, black, red, orange, most of the full spectrum, colorless, iridescent
Crystal habit
Irregular veins, in masses, in nodules
Crystal system
Amorphous
Cleavage
None
Fracture
Conchoidal to uneven
Mohs Scale hardness
5.5–6.5
Luster
Subvitreous to waxy
Polish luster
Vitreous to resinous
Refractive index
1.450 (+.020, -.080) Mexican opal may [...]

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