Rare Orange Benitoite
A bright orange benitoite (figure 1) weighing 2.29 ct was recently examined at the Carlsbad laboratory. Standard gemological testing revealed a refractive index of 1.756 to over the limit (OTL) and a specific gravity of 3.68. The fluorescence reaction was strong orange in long-wave ultraviolet light and medium blue in short-wave UV (figure 2). The benitoite was slightly color-zoned orange and blue; the blue portion’s pleochroism was very light blue and darker blue, while the orange portion’s pleochroism was orangy yellow and dark orange. Microscopic examination showed altered crystals with discoid fractures (figure 3) and strong doubling. The discoid fractures were consistent with heated benitoite.
Benitoite is a barium titanium silicate (BaTiSi3O9) known as the California state gem, and it only occurs in gem quality in San Benito County, California. The New Idria District produces medium to medium-dark blue and lighter blue colors. According to a previous study published in G&G, pink and colorless examples are considered rare. In addition, heat treatment of lighter-color or colorless benitoite may result in an orange color. Since only a small portion of the treated material successfully changes color, orange benitoite is considered rare (B.M. Laurs et al., “Benitoite from the New Idria District, San Benito County, California,” Fall 1997 G&G, pp. 166–187).
This benitoite was faceted by Bill Vance of Vance Gems, who stated that the rough was colorless prior to heat treatment. The bright orange color and large size make this an exceptional example of orange benitoite. Very few of these have been examined at GIA, and this 2.29 ct gemstone is the largest example we have observed.
