Cristobalite, Fayalite, Obsidian
Canyon Butte occurrence (Couger Butte), Canyon Butte, Siskiyou Co., California, USA
Small Cabinet, 5.8 x 5.8 x 4.4 cm
A visual and showy specimen of a 2.5 cm "eye" of high-temperature cristobalite nicely set in highly lustrous, jet-black obsidian from an uncommon California locale - the Couger Butte, Siskiyou County. The "eye" has three clusters of gemmy, olive-green, 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.