BENITOITE  , a

mineral discovered in 1907 near the head-waters of the San Benito river, San Benito Co., California, and described by Prof . G . D . Louderback . It is a titano-silicate of barium (BaTiSi3O9), crystallizing in the hexagonal system, with a hardness of 6.5, and specific gravity 3.65 . It may be colourless or blue, the colour varying sometimes in different parts, and passing to a deep sapphire blue . The blue variety is cut as a gem stone, and often resembles blue spinel, though its softness distinguishes it from spinel and sapphire . It is a brilliant stone, with high refractive index, and is strongly dichroic, being pale when viewed parallel to the principal axis and dark when viewed transversely .