Cristobalite, Fayalite

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A fine specimen featuring "eyes" of high-temperature cristobalite scattered in highly lustrous, jet-black obsidian from an uncommon California locale - Couger Butte, Siskiyou County. Some of the "eyes" have faint hints of gemmy, micro-blades of fayalite, an olivine group mineral. Obsidian (volcanic glass) cools too quickly, to crystallize. Thus, it is unusual to see minerals attached. The "eyes" or spheres of high temperature cristobalite (SiO2) are actually the result of devitrification, or loss of silica from the obsidian. Ex. Mullane Collection.