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.

Six weeks isn’t time enough to find much benitoite. Maybe that’s why, excepting its brief association with Shreve & Co. between 1907 and 1912, this gem has no other history as a jewelry stone-although Tiffany is said to have tried for an exclusive on the mine’s output once the news broke of benitoite’s existence. This lack of jeweler interest is probably for the best, since benitoite’s one major drawback is a hardness of 6.5, the same as tanzanite, that makes it risky for ring use.

In any case, retailer neglect hasn’t hurt benitoite’s status. To the contrary, immediately after it was announced as a new gem, benitoite ignited an ardor in collector circles which is as strong now as ever. Today, estimates Gray, at least 90 percent of all benitoite is sold to collectors-most, until recently, in Europe. Now, however, a fast-growing audience for the gem is found in America.

From an aesthetic standpoint, it’s easy to see why benitoite has endeared itself to collectors. Fine specimens typically feature flattened, triangular gem crystals, rarely more than one inch wide, that are translucent with white centers and blue edges. These crystals either protrude from or are embedded in granular snowy-white masses of natrolite that serve as matrix. The contrast between these distinctive and well-formed benitoite crystals and their host rock is dramatic and impressive.

Further aesthetic delights are revealed once these crystals are extracted (using hydrochloric acid) from the natrolite for faceting. In color, faceted stones most often resemble sapphire and tanzanite, with darker stones more like the later, lighter ones the former. On rare occasion, cut stones are either pink or colorless. Unless stones are overly dark, something rare for this breed, benitoite looks stunningly brilliant-the result of dispersion only a tad less than that of diamond.

Small is All

For those who like their gems to possess girth, benitoite may be a disappointment. Since crystals are usually highly included, only small areas can be cut that are eye-clean. What’s more, the flatness of most benitoite crystals restricts the cutter’s maneuverability and chances for good recovery. Last, best color is attained by cutting along a crystal direction that requires considerable rough to be sacrificed.

Consequently, stones most often finish to sizes between 10 points and slightly over 1 carat-regardless of the size of the crystal from which they originate.

“On average, we cut five stones a year that weigh 2 carats or more,” says Gray. “We’re lucky if we find one crystal every five years that yields a stone over 5 carats.”

To date, the largest faceted benitoite known weighs 7.80 carats and is on display at the Smithsonian Institution in Washington D.C.

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