Benitoite

Benitoite Specimen.
Benitoite Specimen.

Prospectors in the Mt. Diablo range, on the hunt for copper and mercury, spotted this heretofore unknown gem winking up at them from the ground. Denim to violet-blue in color, benitoite is extremely dispersive and can be confused with sapphire or tanzanite by the uninitiated. It clinched its moniker from the only source of facetable specimens, San Benito County, California. 

Shreve & Co. of San Francisco submitted a specimen to George Davis Louderback, a University of California, Berkeley geologist for his observations. In July 1907 he dubbed the new species of stone benitioite. In 1985, California lawmakers recognizing benitoite’s uniqueness and collectible nature, promoted it to the status of California state gem.

Benitoite is very popular with collectors. Desirable specimens have triangular if somewhat flat, gem crystals. The white natrolite matrix highlights the rich blue color creating the perfect backdrop for a showy specimen.

In color, faceted stones most often resemble sapphire and tanzanite, with darker stones more like the latter, 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.1

Gemological Information for Benitoite

Color:Blue or Violet Blue, Rarely Colorless or Pink
Crystal Structure:Hexagonal
Refractive Index:1.757 – 1.804
Durability:Fair
Hardness:6 to 6.5
Family:
Similar Stones:Azurite, Sapphire, Synthetic Sapphire
Treatments:None Known at this Time
Country of Origin:U.S.

Benitoite Care

Ultrasonic Cleaning:Risky
Steam Cleaning:Never
Warm Soapy Water:Safe
Chemical Attack:Attacked by Hydrofluoric Acid and Slowly Slowly Affected by Hydrochloric Acid
Light Sensitivity:Stable
Heat Sensitivity:No Rapid Temperature Changes

Source

  • Federman, David. Gem Profile/2: The Second Sixty. Shawnee Mission, KS: Modern Jeweler, A Vance Corporation Publication, 1992.
  • Gem Reference Guide, Los Angeles: Gemological Institute of America, 1988.
  • Schumann, Walter. Gemstones of the World. New York: Sterling Publishing, Co., 1977.

Further Resources
Gems & Gemology: The Quarterly Journal of The Gemological Institute of America.

Benitoite:

  • Summer 1953, Benitoite, by Ehrmann, p. 317, 1p.
  • Summer 1963, A Beautiful 4 1/2-ct. Benitoite and a Colorless Benitoite, p. 55, 1p.
  • Spring 1968, Pink Benitoite from Calif., p. 284, 2pp.
  • Spring 1968, Benitoite Inclusions, p. 285, 2pp.

Online Texts on Benitoite:

  • 1907, Benitoite, A New California Gem Mineral, by G. D. Louderback, Univ. of Calif. Geol. pub., Vol. 5, #9, pp. 149-153

Notes

  1. Federman, p.21
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