Benitoite fluoresces under short wave ultraviolet light, appearing bright blue to bluish white in color. The vein is a highly mineralized shattered zone in the schistose rock. According to Mr. Couch, specimens given to Harry U. Maxfield, of Fresno, were shown to G. Eacret, of Shreve & Co., San Francisco, and to G. D. Louderback. Transparency: Crystals are transparent to translucent. Of these faces the pyramid Ï generally has the largest development. Other rare gems and minerals include Neptunite, Joaquinite, djurleite, and Natrolite. Benitoite has a specific gravity of 3.65, compared to a specific gravity of 3.9 to 4.1 for sapphire. 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. Benitoites identification and original description was based upon specimens found in the headwaters of the San Benito River, in San Benito County, California, from which it received its name. The birefringence is high and the pleochroism very strong. The Benitoite Gem Mine filled one of the largest voids in the mineral world in spectacular fashion. The natrolite fails and the albite is also less abundant in the hornblende rock at some distance from the vein. Though benitoite has been found in a few other locations in the world (in Arkansas, USA and in Japan and Australia), so far, the only gem-quality specimens have been found in California. This ledge also carries a streak of natrolite with benitoite. following notes are taken from their description. What is Benitoite used for? Tabular dipyramidal crystals. The "glory hole" was excavated in a very large pocket or bulge in the vein, a portion of which may still be seen along the north wall of the open cut. Gem quality stones and unbelievable mineral specimens can only be found one place on earth, a small 40 acre parcel of land in the Diablo Mountain Range of San Benito County California. The mean refractive index of benitoite is greater than that of sapphire, and measures 1.757 to 1.804 (sapphire 1.759 to 1.767). By cutting intensely colored stones with the table only slightly out of parallel to the base, the color may be reduced to a desirable shade. Kay Robertson Collection Here is a beautiful crystal of the Zeolite Group species, Natrolite. Its chemical composition is BaTi(Si3O9). The Dallas Gem Mine in San Benito County is the only place in the world where gem-quality benitoite is found and where benitoite is found in specimen-quality crystals. ). Benito has a deep blue color scheme and wears either the winter or summer uniform depending on the season. Specimens cut by Mr. Eacret were thought to be sapphire. Benitoite is used for a number of different purposes. Most benitoite deposits have been found in California, particularly in San Benito County, and in Arkansas and Japan. Benitoite is another important use as a mineral sample. The width at the mine between the serpentine walls is about 150 feet and at a distance of 150 feet east of the mine it is only about 90 feet; about 80 feet farther east at the apex it is over 100 feet. Dec 10, 2020 - Benitoite is the state gem of California. The natrolite, with which the benitoite and neptunite are associated, does not generally occur in distinct crystals of any size. The following description has been abstracted in part from Doctor Louderback's report and notes supplied from personal observation have been added. Hessel predicted the ditrigonal dipyramidal class of crystallization in 1830, and when minerals were found in San Benito County in 1907 with this crystal habit, his hypothesis was confirmed. 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. Benitoite crystal structure: Crystal structure of benitoite, BaTiSi3O9, P-6c2, projected onto the (a,c) plane. First discovered near the headwaters of the San Benito River in 1907 (hence the name), benitoite is a very rare gem that ranges in color from a light transparent blue to dark, sapphire blue, or occasionally a … It is without a doubt, the rarest Gemstones in the world! Natrolite is a hydrous silicate of sodium and aluminum crystallizing in the orthorhombic system. Specific Gravity: is approximately 3.6 (above average) It is in many places attached to hornblende impregnated with natrolite and is partly or completely inclosed in natrolite on the remaining sides. The mineral’s unique crystals are of great value as collectable samples. 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