There are a lot of things to which the expression “Only in California” is a good fit. Some are sarcastic, some tongue in cheek, and the rest may be positive or positively amusing. There’s also a sparkling addition to the ‘Only in California’ category.
When it comes to gemstones, we love the one-source-only variety. Gemstone rarity is a crowd-puller for die hard collectors. But smack-dab in the old USA, there is a gem-mineral that is not only rare but is truly a one-source gem with regard to its commercial production.
Our Own Stone
Besides the prestige of it being a one-source stone, its beauty is an added bonus. I’m speaking of course about the azure-hued benitoite. Let me expand on that statement just a bit. True, there have been sightings of benitoite elsewhere around the globe. But the only known commercial deposit of gem-quality material rests in the Dallas Claim - popularly known as the Benitoite Gem mine of San Benito County, CA. Geological research points to the odd specimens in Hot Springs County, AR, Fresno County and Kern County, CA. Rare occurrences were also found in Australia, Czech Republic and Japan.
What Collectors Crave
This transparent gem has a lot going for it. Topping the list for aficionados might be its extraordinary dispersion, producing that head-turning fire and brightness that jewelry lovers crave. Its high RI (refractive index) is responsible for this desirable trait. Cutters tell us that proper faceting is essential to show off its extraordinary characteristics.
The story of its discovery goes something like this. In 1907, prospector James Couch set out to investigate some fascinating outcrops to his claim. The area he focused on was littered with little blue bits which he suspected to be sapphire crystals. Giving these to the professor of mineralogy at UC Berkeley, it soon became apparent these were not sapphire at all, but rather a new (Eureka!) mineral unknown to science. In July of that year a published report named the new material benitoite, after the location of its discovery. And for the next 5 years, this mine produced thousands of first-rate benitoite crystals. The demand for the stone waxed and waned over the ensuing decades. From the mid 1980s through 1999, a massive site expansion opened up the area for more recovery of the stones.
In 1985, benitoite was named the California State Gemstone.
With a higher dispersive quality than that of diamond and luxurious hues rivaling the best sapphire, this stone is a mesmerizing choice for collectors. It doesn’t come cheap however. Since many crystals are found in small sizes, the larger stones drive the price up exponentially. Its hardness rates at 6 - 6.5 Mohs, meaning that jewelry can safely be set with these stones. One curious trait this material exhibits is that often its intense blue coloration can mask some of its high dispersion. And that high dispersion can cause benitoite to display the occasional red or green flashes which collectors admire.
Because of its rarity, expert gem cutters might occasionally forfeit their best cut in favor of producing the largest possible yield. This conundrum has lead to polished benitoite stones showing some windowing or less than ideal proportions in faceted goods.
See For Yourself
Still, many collectors would love to get their hands on an American stone and one that’s rare to boot. How desirable is it you ask? Authentic rare stones are always a precursor to its created counterpart. Labs have set out to recreate this stone; but so far, the synthetic results are only colorless and too small for faceting. Since the California mine ceased production in 2005, benitoite crystals have become more desirable than ever for serious collectors.
Most benitoite crystal available today are small; under 1 carat. But some have been produced in the 2 to 3 carat range. Like to see a terrific example of benitoite yourself to really understand this gemstone? For a view of the largest specimen on record, make a trip to the Smithsonian Institution where a 7.8 carat benitoite resides.