Andradite

specimen number:
2133244

location:
Green Fire Mine, San Benito Co., California, USA

description:
Lustrous translucent green crystals of andradite measuring to 0.3 cm in size on matrix. In good condition. This is the variety of the species known as demantoid. Collected by Chuck Trantham.

The Green Fire Mine, located in the New Idria District of San Benito County, California, is the premier North American locality for demantoid, a variety of andradite. Geologically, the deposit is situated within the New Idria Serpentinite Massif, where hydrothermal fluids interacting with ultramafic rocks precipitated rare minerals in fractures and veins. The demantoid found here is a calcium-iron garnet that gains its vibrant green color from traces of chromium, often occurring as brilliant, well-formed dodecahedral crystals perched on a contrasting white chrysotile or gray serpentine matrix. Historically, while the broader New Idria area was famous for mercury and benitoite mining for over a century, the specific exploitation of the Green Fire Mine for demantoid began in the late 1990s and has continued through the 2020s. Unlike many historic industrial mines, it is a small-scale, specialized operation focused entirely on the recovery of gemstone and specimen-grade minerals. California demantoid is highly valued by collectors for its exceptional luster and fire, often rivaling the classic Russian material in quality and intensity of color.

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