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Benitoite

If mining company owner Rod Dallas hadn’t sent two prospectors up into the southern Mt. Diablo range to look for copper and mercury late in 1906, California might not have its state gem today.

The gem is benitoite, named after the stone’s sole source of facetable material in San Benito County, California, near the Fresno County line. Due in part to the fact that it has only one meaningful occurrence, benitoite became California’s state gem in 1985.

It is highly doubtful, however, that the gem would have been awarded such status just because of its rarity. Beauty and gemological uniqueness (it’s the only gem known in its crystal class) played equally decisive roles. In fact, it can be said California’s lawmakers were acknowledging benitoite’s remarkable and swiftly attained stature among gem collectors. Right after it was identified as a new species, benitoite became a paragon among collector gems.

Shiny Blue Pebbles

Like its brethren state gems, Main tourmaline and Montana sapphire, benitoite was found purely by chance. As so often happens, its discoverers were distracted from the pursuit of metals by the chance glimpse of a mineral—in this case, highly reflective blue pebbles lying on the bank of a small mountain stream at a spot some 4,000 feet above sea level. “It would have been hard not to notice these gems,” explains author Peter Bancroft, who devoted an entire chapter of his 1984 book, “Gem and Crystal Treasures,” to benitoite and who explored for the gem in the 1930s. “Benitoite is found in dry, scrub-infested country where serpentine [a very soft, flaky mineral with a dull green color] is the predominant base rock. Given this terrain, anything bright and shiny would stand out.”

Benitoite is certainly bright and shiny. But even among the ranks of the radiant, few colored stones exhibited brilliance as great as those from the new deposit in California’s Coast Range. So while its denim- to violet-blue colors at first led many jewelers to mistake it for sapphire, some who were intrigued by its unusually high dispersion suspected it was something else altogether.

One skeptic at Shreve & Co., the San Francisco jewelry store that was to be the mystery gem’s earliest marketer, persuaded his superiors to send samples to George Davis Louderback, a geologist at the University of California, Berkeley, for study. In July 1907, he published the first of two papers on the stones, identifying them as a new species that he named “benitoite” for its geographic origin. The name has proven apt since no other deposit—let alone source—of facetable benitoite has ever been found.

For Collectors Only

What is now known simply as the Benitoite Mine is very small. Bill Forrest and Buss Gray, who have owned the mine since 1987, are convinced that if it had been worked all year round once discovered, it would have run dry decades ago. They ought to know, since they’ve worked the mine longer than anyone else—leasing it for 20 years before buying it. For them, a mining season lasts five or six weeks, usually in March and April. “Lack of water becomes so severe a problem by May that we must shut down operations,” Gray says.

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Benitoite