The chemical and physical properties of benitoite and its associated minerals have been described by Louderback and Blasdale, and the following notes are taken from their description. The chemical analyses show it to be an acid barium titano-silicate corresponding to the formula BaTiSi3O9 . Benitoite is insoluble in ordinary acids, but is attacked by hydrofluoric acid…

The benitoite is obtained by breaking open masses of vein rock and carefully chiseling or working the crystals out of the inclosing natrolite. Many gems are injured or ruined by this method. The removal of the natrolite by acid has been tried with partial success. Large slabs of rock 2 to 3 or more feet across are obtained coated…

The benitoite occurs with neptunite in crusts, seams, and thicker deposits of white natrolite on the walls of geode-like cavities and fissures in the hornblende schist. These deposits occur in both irregularly shaped masses and in seams with more definite directions. They inclose fragments of hornblende schist which has been heavily impregnated with natrolite. In some…

Development work at the benitoite mine at the time of the writer’s visit consisted of a large and a small open cut, a prospect drift or tunnel with a crosscut tunnel, and an incline shaft. The large open cut or “glory hole” was 20 to 45 feet wide, 85 feet long, and from a few…

The benitoite deposit occurs in a large area of serpentine which extends many miles northward past the New Idria quicksilver mine and a few miles southward, and forms the summit of an anticlinal ridge pitching down to Coalinga. This serpentine is of the usual type of the Coast Ranges and presents different phases from hard dark-green and…

The benitoite mine is in the southeastern part of San Benito County, near the Fresno County line. The deposit is about 35 miles by road northwest of Coalinga in the Diablo Range, about three-fourths of a mile south of Santa Rita Peak, and on one of the tributaries of San Benito River. The elevation of…

The difficulty mentioned by Doctor Louderback in learning who was the original discoverer of the benitoite property was encountered by the writer. It is evident that J. M. Couch, of Coalinga, grubstaked by R. W. Dallas, was instrumental in finding the deposit. Whether he discovered it while out alone or on a second trip with…

The information below is a verbatim transcript of an article about the discovery, geology, mining and properties of benitoite, by Douglas B. Sterrett. It was published in the 1909 edition of Mineral Resources of the United States, by the United States Geological Survey. [2] Description of Benitoite An excellent description of the new California gem mineral,…

Benitoite has an appearance that is very similar to sapphire. Its blue color and pleochroism are very much like sapphire’s. Benitoite and sapphire have overlapping refractive indices, but benitoite has a much higher birefringence, which often shows birefringence blink. Sapphire has a Mohs hardness of 9, while benitoite is much softer at 6 to 6.5. Benitoite has a…

Benitoite is an extremely rare mineral that is best known for being the official state gemstone of California. It is a barium titanium silicate mineral, usually blue in color, that is found in rocks that have been altered by hydrothermal metamorphism. Its chemical composition is BaTi(Si3O9). Benitoite’s identification and original description was based upon specimens found in the headwaters of…