Forsterite

specimen number:
2102413

location:
San Carlos, Gila Co., Arizona, USA

description:
Translucent green forsterite throughout this basalt matrix. This is the variety often called peridot. Classic locality for this material.

The San Carlos area, situated within Gila County, Arizona, is a gem-producing region celebrated for its extensive extraction of peridot, a gem-quality green variety of the magnesium iron silicate mineral forsterite. Geologically, the deposit is hosted within late Cenozoic-aged volcanic fields, specifically the Peridot Mesa basalt flow, where deep-mantle tectonic processes generated ultramafic xenoliths known as peridotite or lherzolite nodules. These dense nodules were transported to the surface by ascending basaltic lavas, creating localized zones tightly packed with individual olivine crystals and granular aggregates within the basalt matrix. Commercial mining operations began in the early twentieth century, around 1900, on the San Carlos Apache Reservation, where extraction is managed exclusively by tribal members utilizing traditional, manual open-pit quarrying and hand-sorting methods to preserve crystal integrity. The deposit has maintained continuous, active production for well over a century and remains one of the premier, high-volume global sources for gem peridot today.

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