Benitoite crystals may vary widely in appearance. While some of the crystals are gemmy and deep blue, most of the crystals are translucent with white centers encircled by blue outer rims. Crystals being 2.5 cm across are considered to be large, and the average sizes are in the range of 1 cm to 1.5 cm. Considerable variation exists in the shapes of benitoite crystals but benitoite most commonly forms as 'triply terminated' crystals, belonging to the ditrigonal-dipyramidal class. Most benitoite crystals are blue and strongly dichroic (colorless to deep blue) with the deepest color occurring in the plane is for parallel to the c-axis. The colors of faceted benitoite gems include: colorless, pale blue, royal blue, deep purplish-blue. Pinkish crystals have also been found but they are extremely rare.
Benitoite fluoresces blue-white under ultraviolet light. Under short wave ultraviolet light the white cores of the crystals fluoresce brighter than do the blue edges. Under long wave ultraviolet light the white cores fluoresce a dull red, while the rims of the crystals are non-fluorescent.
The Benitoite Gem mine is located on a small mining claim (the Dallas claim) in San Benito County, California, about halfway between Los Angeles and San Francisco. Access to the mine is via either a roughly sealed trail that is privately controlled or by two alternate dirt roads that approach from the west and north of the gem mine. This area of the coastal range is sparsely populated and remote with no facilities within miles of the mine.
A prospector name James Couch, was grubstaked by Roderick Dallas, and in February of 1907, and on his way to investigate some intriguing outcrops, he found a small area littered with blue crystals which he thought might be blue sapphires. He collected several and rushed back to Coalinga. A claim was placed which was named the Dallas Gem mine. Dr. George Louderback, a professor of mineralogy at the University of California, Berkeley, was provided with some of the stones. Dr. Louderback soon realized that they were not sapphires or spinel as originally thought, but rather a new mineral unknown at the time. In July 1907 he published an article, naming the new mineral benitoite, after the San Benito County locality.
When word got out of the new discovery, several people, including Dr. George Kunz from Tiffany's of New York, rushed to the site to secure an exclusive marketing agreement with the miners but Mr. G. Eacret, of Shreves and Company in San Francisco was the first to secure the marketing rights.
The mine owner, Mr. R.W. Dallas, built a mine camp and immediately expanded mining operations. The mine produced benitoite from an open cut in the hillside, as well as a short underground tunnel pushed into an outcrop of benitoite bearing that they referred to as blue schist. This blue schist layer yielded thousands of excellent gemstones over a 5 year period.
In 1912, the market for Benitoite slackened and, coming upon difficult financial times, Mr. Dallas closed the mine. The mine was re-opened briefly in 1933, and additional material was discovered. Over the years, the mine's dumps became famous within mineral club circles as a place to collect stone but nice samples became increasingly hard to find.
Between 1933 and 1967, the Dallas family leased the mine to various individuals who worked the mine for gemstones but very little gem material was produced during this period. In 1967, two new serious collectors came to the scene. Elvis “Buzz” Grey and Bill Forrest were able to secure a lease on the Benitoite property and they eventually purchased the property in 1987.
From 1987 to 1999, the property was dramatically expanded, tested and mined. During this period the size of the deposit was more accurately determined and viable areas were exposed. Much excellent gemstone and specimen material was produced. This flurry of activity during the 80's and 90's attracted a number of larger mining concerns and the property was studied and mapped for its gemstone potential. Hundreds of feet of diamond drilling and dozens of test pits proved the existence of economical gemstone reserves.
In 2000, the property was purchased by Benitoite Mining, Inc., a company affiliated with Collector's Edge Minerals, Inc., headquartered in Golden, Colorado. Benitoite Mining, Inc. (BMI) operated a processing plant that separated the gemstones from the properties' eluvial material. Eluvial material is the weathered remains of bedrock. The bedrock weathers naturally through time and then lies in place on the hillside. One result of the weathering was the formation of clay that would entrain the soils containing pebbles and occasional benitoite crystals.
CEMI purchased some of their initial processing equipment from the previous owner. Work involved reprocessing the old mine dumps and mining along the weathered yet to be mined formations. Old tunnels were re opened and then dug out for processing. Further refinement was implemented to improve gem recovery. As it turned out, benitoite is slightly magnetic, due to its iron content. This permitted easy separation of the benitoite from the tailings, and even separation of the facet grade fractions from non-gem benitoite.
The Benitoite Gem mine is the only commercial source of gem-quality benitoite in the world. From the time of its discovery in 1907 until 1967, when Forrest and Gray began working the mine, it is estimated that only about 2,500 carats of faceted benitoite were produced. Of that amount, nearly 1,000 carats were produced during the period of active mining between 1907 and 1911, based on the amount of rough reported in the Dallas Mining Company's account books.
Few stones exceeded 3 ct, and most of the gems weighed less than 1 ct. The balance of 1,500 carats, is believed to have been recovered between 1911 and 1967. Most of these stones were faceted by cutters in the United States, and weights of up to 5 ct were obtained. From 1968 to 1997, Forrest and Gray produced approximately 2,000 carats of faceted benitoite. Most of the stones weight less than and only 500-600 1ct.+ stones and only 15 stones exceeded 4cts. Thus, 89% of the stones were under 1 ct. This relatively low output, compared to other gem mining operations, demonstrates the extreme rarity of this gem material.