CALIFORNIA GEOLOGICAL SURVEY NOTE BENITOITE 11 CALIFORNIA STATE GEM Benitoite (pronounced beh-nee-tow-ite) can occur of blue and colorless. A variety of colors and hues in rich blue crystals that are as striking and flaw- in a crystal is common. Color is often zoned and less as the finest sapphires. Gem quality benitoite is most intense toward the edges of the flattened is found only in a small area of San Benito triangular crystals and pale, white or colorless in County, California. It has never been found in the center. Most of the crystals are translucent and quantity or as crystals much larger than 5 cm have pale blue or white centers with deep blue across. The scarcity of this beautiful gem makes it outer rims. A small amount of iron detected by primarily a collector's item. However, a minor emission spectroscopy may occur in deep blue- amount of high quality benitoite is used to help purple crystals. The violet-blue in some crystals is align and adjust electron microprobe beams. thought to be caused by titanium sesquioxide. Benitoite was discovered in 1906 by J.M. Couch Benitoite fluoresces a bright deep sky blue under at the now well-known Benitoite Gem Mine in short wave ultraviolet light and x-rays. It's one of San Benito County. The mineral was thought to the most beautiful fluorescent minerals. At the be sapphire, but jewelers determined that it tips of many benitoite crystals, the blue daylight wasn't. In 1907, George D. Louderback, a miner- color of the crystal sometimes gives way to white. alogy professor at the University of California These white sections frequently fluoresce pink- identified it as a new mineral species, and named red, sometimes fairly brightly, under long wave it benitoite after the river, county and nearby ultrawave light. A crystal may look blue if seen mountain range where it was found. through the acute faces of the rhombohedron and, when viewed through the obtuse faces it may look Benitoite crystals occur in a wide range of colors colorless. including heliotrope, pink, white, several shades SIDE VIEW TOP VIEW A common crystal habit of benitoite CALIFORNIA GEOLOGICAL SURVEY Revised 5/2002 ©California Department of Conservation, California Geological Survey, 2002. Reproduction of this CGS Note for classroom or public education purposes is encouraged and does not require written permission. However, please cite California Geological Survey as source. The Department of Conservation makes no warranties as to the suitability of this product for any particular purpose. Printed with soy ink on recycled paper. PAGE 2 BENITOITE FACTS Color: Blue, purple, heliotrope, pink, Crystal Form: Hexagonal system. Ditrigonal- white, colorless, often varicol- Dipyramidial class. ored in a single crystal. Fluo- resces bluish under shortwave Hardness: 6-6 1/2 ultraviolet light and x-rays. Luster: Vitreous to subadamantine Mode of Occurrence: Occurs as superb crystals near the headwaters of the San Specific gravity: 3.64-3.69 Benito River, San Benito County. It also occurs in Eocene Cleavage: Poor pyramidal or indistinct, sands in southwest Texas and in fracture concoidal or uneven, sands of the Owithe Valley in brittle. Belgium. Habit: Crystals pyramidal, stubby, or Environment of Occurs as crystals in veins in the tabular, usually flattened along Formation: brecciated zone of a blue schist the c-axis, somewhat triangular. emplacement in serpentine. It's found with neptunite and joaquinite and is encased in a matrix of white natrolite. San Benito County Composition: BaTiSi3O9 (Barium Titanium Silicate) Graphics by Dinah D. Maldonado, California Geological Survey. Offices of the California Geological Survey Publications and Information Office Southern California Regional Office Bay Area Regional Office 801 K Street, MS 14-33 655 South Hope Street, Suite 700 185 Berry Street, Suite 210 Sacramento, CA 95814-3532 Los Angeles, CA 90017-3231 San Francisco, CA 94107-1728 (916) 445-5716 (213) 239-0878 (415) 904-7707 Visit the California State Mining and Mineral Museum in Mariposa, along historic Highway 49. P.O. Box 1192 Mariposa, CA 95338 (209) 742-7625 www.conservation.ca.gov THE RESOURCES AGENCY STATE OF CALIFORNIA DEPARTMENT OF CONSERVATION MARY NICHOLS GRAY DAVIS DARRYL YOUNG SECRETARY FOR RESOURCES GOVERNOR DIRECTOR.