Benitoite

Most benitoite is uncovered in specimens of bi-pyramidal blue crystals in white natrolite. Soaking the piece in acid dissolves the natrolite but leaves the benitoite unaffected. Specimens like the one on the facing page—which contains cuttable gem material—generally range in value from $1,500 to $2,000. The 14k yellow gold strip bracelet is set with 5 cts. t.w. of benitoite round brilliants. The platinum ring, designed by Bradley Stewart, is bezel set with five round brilliants weighing 1.26 cts. t.w. The four loose gems show off benitoite’s true color. The round brilliant weighs 2.5 cts., the cushion cut weighs 1.38 cts., the heart shape weighs 2 cts., and the octagon weighs 1.91 cts.

What more can you ask than for a bright vivid blue dispersive, unenhanced gem mined in America? How about a few more of them?

Benitoite, California’s state gem, fits that description to a T, but up until now, it’s been rare. Since it was discovered back in the early 1900s, reportedly less than 10,000 carats have been cut and polished. Today, however, melee to half-carat stones have been recovered in much greater numbers. Paul Cory of Iteco Inc., Powell, Ohio, reports that in 2002 the mine produced more than 1,500 carats of melee. It’s estimated that the mine can actually produce in excess of 2,500 carats of melee per year. Although this number is small compared with sapphire, tanzanite, or ruby, it’s significant because a single year of mining might produce nearly 25% of the previous 90 years’ output. (Quantities are still tight on stones weighing more than a carat.)

Found in the New Idria district of San Benito County, benitoite has been unearthed in a half-dozen or so mines situated on the slopes of the Diablo Mountain Range. Looking at the map, the mines are in the southern portion of Northern California, 162 miles south-southeast of San Francisco. That also places the mines just a scant 35 miles north of Coalinga, site of the original benitoite mining company as well as the famous Coalinga fault line. In 1983, a 6.7 earthquake destroyed more than 800 homes and was felt as far away as Los Angeles and western Nevada. But despite the shaky ground, the rare benitoite remains locked in hard rock.

History. In 1907, L.B. Hawkins and Jim Couch—both prospectors for an oilman named R.W. Dallas—claimed they had discovered the blue gem. When they first found the stones, they had no idea what they’d discovered. They sent samples of the stones to George Louderback (1874-1957), professor of mineralogy at the University of California at Berkley. It was Louderback who identified it as a new mineral and named it benitoite.

“It has been found very difficult to determine just who is the discoverer of this interesting deposit,” wrote Louderback. “Different individuals have laid claim to this title, and a comparison of their various accounts shows that the ambition to be so called has led to misrepresentations of the facts.” Louderback went on to say, “Mr. J.M. Couch, a prospector of Coalinga, grubstaked by Mr. Dallas, had in December found some deposits that seemed to need further examination, and Mr. Dallas induced Mr. L.B. Hawkins of Los Angeles to accompany Couch into the mountains for that purpose. While out to examine some copper prospects, they happened on the benitoite deposit, and each claims to be responsible for the discovery. Having no idea of the nature of the material, they took some back to town for further enlightenment. At first the idea, expressed by some ‘expert’ in Los Angeles, prevailed that the material was volcanic glass and of no value. Later some stones were cut in San Francisco, the lapidary believing that they were sapphires, and for some time the property was known as the Sapphire Mine.”

Prospecting was a familiar sight in the area, as prospectors focused on minerals such as asbestos, chromium, and of course—this being Northern California—gold. (Note: Louderback became famous not only for his identification of the new gem but also for his study of earthquakes. Louderback was one of the founders of the Seismological Society of America.)

Benitoite has been found in nine different localities throughout the world, including Japan, Australia, and Hot Springs, Ark. But San Benito County is acknowledged as the only source of gem-quality benitoite in the world.

The original mine was owned by R.W. Dallas and his family up until 1987. William Forrest and Elvis “Buzz” Gray leased the property for 20 years before buying it in 1987. In 1997, Gray estimated that up until that time, only 5,000 carats of faceted material had been produced.

Forrest and Gray sold the mine to Benitoite Mining Inc. of Golden, Colo. The new owner, Bryan Lees, is a name you may recognize: Lees also is mining the rhodochrosite Sweet Home deposit. (See “Jewel of the Month,” JCK, June 2003, p. 103.) Lees recently moved a screening and washing processing plant onto the site and is reportedly processing 150 tons per day of benitoite-bearing rock from which the gem material is extracted. The resulting gravel transported by conveyor belt is hand sorted for potential mineral specimens. Magnetic separation is something new to the recovery process. Benitoite is the only mineral recovered at the mine that does not contain any iron whatsoever. Therefore, Lees can recover 100% of the benitoite simply by attracting everything else to magnets and having the non-magnetic benitoite go into separate sorting chambers.

Color. Benitoite, named California’s state gem in 1985, is a blue barium titanium silicate. Some think the titanium content is responsible for the color, as is the case with sapphire, but it hasn’t been proven. The cause of the color is still the subject of debate and study.

That noted, benitoite is seen in a somewhat limited range of colors, from colorless to light blue to deep violetish-blue. There are a few very rare pink and heat-treated orange specimens, as well as bicolor gems. Since it’s often seen in a medium-dark violetish-blue, benitoite looks—at first glance—like a nice Ceylon sapphire.

Qualities. Color is the key factor. It’s considered a class II stone, having inclusions similar in number and size to those of sapphire. Size is another value consideration: Benitoite doesn’t get very big. The largest gem cut in 2001 weighed 3.55 cts.

Enhancements. Benitoite is traditionally unenhanced.

Pricing. Faceted benitoites are comparable in price to fine sapphires, even though they are far more rare. According to The Guide, extra-fine-quality .5-ct. benitoites are priced from $500 to $750 per carat, and 1-ct. to 2-ct. extra-fine benitoites are priced from $1,500 to $3,000 per carat.

Care and cleaning. With a hardness of only 6-6.5 (similar to tanzanite and peridot), benitoite can be abraded through wear. Take extra precautions to avoid scratching the gem when cleaning. Always wash off dust, which will typically have a hardness of 7, before wiping with a cleaning cloth. Dust can scratch, and that will dull the luster of the gem.

Bench precautions. Repair-temperature heat should not be applied to the stone, as some benitoites have changed from blue to orange after being exposed to heat treatments. Heat from the ultrasonic or from steam cleaning, however, will not affect color.

Recommended reading. For more information, see “Benitoite from the New Idria District, San Benito County, California,” by Brendan Laurs, William Rohtert, and Michael Gray, GIA, Fall 1997, Gems & Gemology; and Gem & Crystal Treasures, by Peter Bancroft, The Mineralogical Record, 1984.

Special thanks to Bryan Lees, Benitoite Mining, and Paul Cory of Iteco, (614) 923-0080,www.itecoinc.com.