Cristobalite and Fayalite in Obsidian (Mullane Coll.)

Item Description

A visual and showy specimen of a 2.7 cm, tan, "eye" of high-temperature cristobalite jauntily perched in highly lustrous, jet-black obsidian from an uncommon California locale - Cougar Butte, Siskiyou County. The "eye" has faint hints of gemmy, micro-blades of olive-green 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 and dates from the 1950s to early 70s.