Cristobalite, Fayalite

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A visual and fine cabinet specimen of "eyes" of high-temperature cristobalite scattered in highly lustrous, jet-black obsidian from an uncommon California locale - Cougar 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. Certainly, a most unusual and uncommon specimen. Ex. Mullane Collection.