Benitoite

specimen number:
1115245

location:
Dallas Gem Mine, San Benito Co., California, USA

description:

A superb thumbnail for the species, a sharp semi lustrous slightly translucent grouping of benitoite crystals. This is in super condition.

The Dallas Gem mine (historically known as the Benitoite Gem mine), situated near the headwaters of the San Benito River in the remote Diablo Range of San Benito County, California, United States, is an internationally famous underground and open-pit operation renowned as the premier source of the exceptionally rare barium titanium silicate mineral, benitoite. Geologically, this highly localized deposit is situated within the New Idria serpentinite body, where high-pressure, low-temperature metamorphic processes generated tectonic blocks of glaucophane-bearing blueschist. Late-stage hydrothermal fluids rich in barium, titanium, and silica migrated through structural fractures in this blueschist, precipitating lustrous, sapphire-blue triangular crystals of benitoite, black prismatic neptunite, and honey-brown joaquinite, all completely embedded within a younger, dense matrix of white natrolite. Historically, the deposit was discovered in early 1907 by prospector James Marshall Couch, who was financially backed by Roderic W. Dallas, leading to the rapid formation of the Dallas Mining Company and the initiation of formal open-cut and underground tunneling in July 1907. The mine operated with high intensity until 1912 when commercial extraction became temporarily uneconomical, after which the property experienced decades of intermittent leasing, illicit digging, and bulldozer-assisted tailings reworking by various operators, including Clarence Cole from 1952 to 1967 and the team of Bill Forrest and Buzz Gray from 1967 until its acquisition by Collector's Edge in 2001. Following a thorough, highly systematic mechanized excavation of the remaining underground vein system that proved the primary ore body was entirely exhausted, all large-scale commercial extraction permanently ceased in 2005, and the site was reclaimed. Through 2026, while the locality operates strictly as a small, fee-based pay-to-dig tourist site for collectors screening old dump material, benitoite stands proudly as the official California State Gemstone, and specimens preserved from the historic Dallas workings remain the absolute global mineralogical benchmark for studying blueschist-hosted silicate crystallization.

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