Description

Color is colorless or white. Luster is vitreous. Transparency: Crystals are transparent to translucent. Crystal System is tetragonal; 4 2 2 (alpha cristobalite) and isometric; 4/m bar 3 2/m (beta cristobalite). Crystal Habit includes the always small (usually microscopic) and rarely well formed crystals that are pseudo-isometric, being pseudomorphs of beta cristobalite. The crystals are typically pseudo-octahedrons, some of which are twinned in a special twin called the spinel twin. The more commonly observed habit is radiating clusters and spherical aggregates. Cleavage is absent. Fracture is conchoidal. Hardness is 6.5 Specific Gravity is 2.*2+ (below average for translucent minerals) Streak is clear. Other Characteristics: Refractive index is approximately 1.*8 Best Field Indicators are crystal habit, environment of formation (mostly in the crevices of volcanic rocks), color and index of refraction. Site design & programming by ***** web services