The strike encountered in the tunnel, about 30 feet lower and to the north, was nearly cast and west with a dip of about 40Â° N. In the upper part of the face of the open cut the dip was high, about 65Â° N., and below the middle of the face it was low, 15Â° to 25Â° N. Along the north side of the open cut and in the lower cut the strike was about east and west and the dip was probably rather low, 20Â° to 30Â° N. These measurements do not agree closely with those of Doctor Louderback, especially in regard to the dip of the vein. In the latter places the benitoite projects into the cavities along with the coarse drusy surfaces of the natrolite. Clarity improves quality, particularly eye clean or better scores. The color of benitoite is not affected by heating the stone to redness and allowing to cool. Benitoite has been found in bowlders a few hundred yards west of the mine on the hillside and in the creek. Luster: is vitreous. The most widely used minerals are: natrolite, neptunite, joaquinite, serpentine and albite. These phases were probably originally different adjacent formations that have been metamorphosed. Under short wave ultraviolet light, benitoite fluoresces which appear bright blue to bluish white in colour. Cabochon-cut gems from crystals with color variations or partially flawed material have some beauty. Benitoite and sapphire have overlapping refractive indices, but benitoite has a much higher birefringence, which often shows birefringence blink. Cleavage: is absent. The benitoite is obtained by breaking open masses of vein rock and carefully chiseling or working the crystals out of the inclosing natrolite. Benitoite fluoresces under short wave ultraviolet light, appearing bright blue to … The natrolite did not permeate far into the rock, but formed a coating on the walls of the fissures. Typically, benitoite occurs in combination with minerals which make up the host rock. The following description has been abstracted in part from Doctor Louderback's report and notes supplied from personal observation have been added. Benitoite fluoresces under short wave ultraviolet light, appearing light blue in color. Pale-colored stones should be cut with the table perpendicular to the base or parallel to the vertical axis of the crystal to secure the full color value. Part of the massive form is a dark-gray to greenish-gray rock that might be called trap. 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). The unfilled cavities and seams in the vein zone aided by later fractures and faults has offered an easy passage for more recent decomposing meteoric waters. This gives the crystal a triangular aspect with the corners truncated
It occurs in black to reddish- black prismatic crystals of the monoclinic system, the length commonly being several times the thickness. The benitoite mine is in the southeastern part of San Benito County, near the Fresno County line. The fault was directly across the schistosity with a north-south strike and a. dip of 45Â° W. This prospect tunnel encountered a little natrolite (vein material) in the hornblende schist in its upper west side, 15 feet beyond the crosscut tunnel, which crossed a small streak of vein material containing a little benitoite about 10 feet from the main tunnel. Overview Benitoite is one of the rarest gemstones in the world. The specimen is from the Dallas Gem Mine, San Benito River headwaters area, New Idria District, Diablo Range, San Benito County, California. The failure might also be due to the pinching out of the vein a short distance below the large pocket opened in the "glory hole." Many of the crystals are naturally etched on one or more sets of faces. 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. They inclose fragments of hornblende schist which has been heavily impregnated with natrolite. Associated with serpentine and albite, but more importantly with rare minerals such as natrolite, joaquinite, and neptunite. On a chemical level, it is classified as a barium titanium silicate mineral. Other rare gems and minerals include Neptunite, Joaquinite, djurleite, and Natrolite. The mineral exhibits a brilliant blue color under ultraviolet radiation. Benitoite is a rare blue gemstone that is found in only one location on earth, San Benito county, California, USA. Natrolite is a hydrous silicate of sodium and aluminum crystallizing in the orthorhombic system. Corundum (sapphire) has a Mohs hardness specified at 9, while benitoite is much softer. The vast majority of crossite included are floaters with complete terminations on … Small amounts of benitoite have also been found at other locations in California, Arkansas, Montana, Australia, Czech Republic, Japan, and Romania. Other forms are rather rare and of small importance. Doctor Louderback found the material to be a new mineral and named it benitoite after the county in which it was found. 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. Benitoite is a rare blue silicate mineral, found in hydrothermally altered serpentinite. These facts point to the same period of formation for the three minerals with the power of crystallization arranged in the following order: neptunite, benitoite, and natrolite. The outcrop of rock on the north side of the vein zone, on the summit of the ridge, is of a similar nature and has been mentioned above as diabase or gabbro. 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. The minerals Albite, joaquinite, natrolite, neptunite and serpentine occur mainly with this. While the mineral benitoite itself is quite rare, large gem-grade crystals have only been found in one very small region of California, and in commercial quantities only on one small hill in San Benito County. Benitoite has a specific gravity of 3.65, compared to a specific gravity of 3.9 to 4.1 for sapphire. Benitoite (be-NEE-toe-ite) is interesting and unique from a number of viewpoints. Transparency: Crystals are transparent to translucent. The large open cut or "glory hole" was 20 to 45 feet wide, 85 feet long, and from a few feet to 35 feet deep; it had a north of east direction into the hillside. 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. Where can I find Benitoite in California? 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 therefore necessary to remove the natrolite with acid (HCl) to expose the crystals of benitoite. Virtually all collectors specimens for this mineral are from this area. Often the inclosing crust or shell of white natrolite can be split from a crystal of neptunite or benitoite in two or three large pieces, so that the covering can readily be replaced over the crystal. Photo by TheGemTrader.com. . Benitoiteâs 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. So far benitoite has been found at one place only. It has a prismatic cleavage and the thin splinters or powder show a deep reddish-brown color. USA hand faceted, no treatments. Tabular dipyramidal crystals. In the cavities the natrolite occurs in simple well-developed white columnar crystals up to a centimeter or more in thickness and several times as long. He named it benitoite for its occurrence near the headwaters of the San Benito River in San Benito County, California. There is a mountain range of basalt, chert, gray wack, shale, serpentine and Cretan and Tertiarian sandstones at the southern end or at the “Diablus Range.” It is a mountainous belt. How do you identify Benitoite? 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. Rock hounds, gem and specimen hunters, this is your chance to find one of the rarest and most desirable gemstones in the world! This schist inclusion has been described by Kalph Arnold as 150 feet wide at its widest point and at least 1,200 feet long. Why is benitoite a state gem in california? Benitoite has never been found in quantity or as crystals much larger than 5cm across. The prism faces are narrow, though generally present. Its blue color and pleochroism are very much like sapphireâs. A collectors gemstone, a high end fashion gemstone. It gets its name from San Benito County, California where it was first found. The incline shaft was apparently sunk in the lower part of this outcrop and did not encounter benitoite. Beniotite is a very rare mineral that was discovered in 1907 in San Benito County in California. The strike of the ledge outcropping to the east of the open cut was about N. 60Â° W., with a high northerly dip. Bismuth Crystal “Artificially grown bismuth crystal”, Incredible moment Anak Krakatau erupts, Oct 2018, Otman Bozdagh Mud Volcano Eruption “Sep23, 2018”, SAGA GIS – System for Automated Geoscientific Analyses, ParaView “Open Source Visualization For Geoscience”, Scientists and philosopher team up, propose a new way to categorize minerals, Geoscientists use zircon to trace origin of Earth’s continents, Donwilhelmsite : New mineral from the moon could explain what happens in the Earth’s mantle, Chrysoberyl : One of the world’s most expensive Gemstone, Volcanic eruptions may explain Denmark’s giant mystery crystals. The beautiful color, brilliancy, and fire of the gem, however, adapt it to other classes of fine jewelry. Rock hounds, gem and specimen hunters, this is your chance to find one of the rarest and most desirable gemstones in the world! Benitoite is insoluble in ordinary acids, but is attacked by hydrofluoric acid and dissolves in fused sodium carbonate. The Benitoite Gem Mine filled one of the largest voids in the mineral world in spectacular fashion. The vein and the schist in this cut were much blackened and stained with films and seams of manganese dioxide. The use of benitoite in rings or jewelry subjected to hard wear is limited by its comparative softness. The prospect tunnel was driven 120 feet in a direction N. 70Â° E. from the end of the large open cut. The impression gained by a study of the deposit and by plotting the location of the vein where encountered in different places was that the deposit consists of an ore shoot pitching to the west and lying in a fracture zone in hornblende schist with an irregular east and west strike and north dip. J. M. Couch, one of the original discoverers of the benitoite deposit, has located several prospects in formations resembling that at the benitoite mine. The benitoite mine is in the south side of this spur, about 50 feet lower than the apex and 250 feet west of it. The schist near the vein is composed of bluish hornblende and actinolite needles penetrating granular masses of albite. Where can benitoite be found? In some specimens the following minerals are determinable under the microscope: augite, plagioclase crushed and recrystallized and containing clinozoisite prisms, secondary albite, yellow serpentine, and a little titanite and pyrite. How much is Benitoite worth? The California State Gemstone, Benitoite.  The only location where gem-quality material has been found is in San Benito County, California. 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. Benitoite is the state gemstone of California. This gem is almost always blue (it was originally thought to be a sapphire) but also has variations in purple, pink, and clear. Typically color zoned, Benitoite comes in various shades of blue to white and, occasionally, colorless or pinkish. prisms m(1010), and n(0110), and the trigonal pyramids p(1011) and Ï(0111). The hornblende occurs in minute needles, felted masses of needles, blades, and stouter prisms. The albite permeated the rock for many feet each side of the fracture zone. The only significant locality for Benitoite is the Diablo Range, near the headwaters of the San Benito River, in the Southern tip of San Benito Co., California. The meaning of the name of this stone relates to the location where they were first found, in a 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. The removal of the natrolite by acid has been tried with partial success. A specimen was sent to the University of California, Berkeley in 1909 where mineralogist Dr. George D. Louderback discovered it was a mineral that was previously unknown. When viewed parallel to the vertical axis, or perpendicular to the base, the two rays are colorless and remain so while the dichroscope is rotated. The end of the southward extension of this ridge is a low knob about 160 feet above the creek. Many gems are injured or ruined by this method. It is a barium titanium silicate mineral, typically of a blue color, found in hydrothermal rocks with a chemical composition of Ba Ti(Si 3O9). Under long-wave UV light, the clearer to white benitoite crystals fluoresce green. The fractures and joints with the vein filling are about parallel with the schistosity of the rock, which averages nearly east and west in strike with local variations and has a varying dip of 20Â° to 70Â° N. A sketch map of a small area on the benitoite mine hill giving the outcrops with their dips and strikes and the formations encountered in the mine workings shows the schist and gabbro inclusion in the serpentine to be quite irregular in shape. A couple of other regions where the stone is found does not have gem-quality crystals of Benitoite… Most specimens are violetish-blue. Benitoite is also found, frequently, as gray to greenish colored crystals with very heavy inclusions of the amphibole crossite. This rock also incloses crystals of natrolite showing that part of it was formed later than or during the crystallization of the natrolite. These have a bluish to yellowish green to nearly colorless pleochroism, and are in part probably actinolite and in part glaucophane or allied hornblende. Such faces are a little dulled or slightly pitted. Color variations are common in the same crystal, and the change from dark to light blue or colorless may be sharp or gradual. Color: is typically blue, but also colorless and yellowish. Benitoite is a very rare and beautiful dark blue gemstone. This locality was for years the only one from which this species was taken. Faceted Benitoite: Five tiny gems of faceted benitoite in a color gradient set from nearly colorless to violetish-blue. The more schistose phases are grayish-blue to blue and grade into vein material. The most widely used minerals are: natrolite, neptunite, joaquinite, serpentine and albite. The mine has gone by many names over it's 106 year history. In the early days of mining at the Dallas Mine, the hardness of the matrix was a great source of frustration to the miners. Doctor Louderback mentions the outcrop of spheroidal gabbro on the southeast of the benitoite deposit on the hillside. This ledge also carries a streak of natrolite with benitoite. Slickenside seams and lentil-shaped blocks and masses are common through the serpentine, much of which is decomposed near the surface and breaks down to light grayish-green soil which has a greasy feeling when rubbed between the fingers. If you have spent any time viewing any of my websites you know that I have a passion for BaTiSi 3 O 9 also known as Benitoite. According to Doctor Louderback the largest perfect stone so far cut weighs over 7 carats and is about three times as heavy as the next largest flawless gem so far obtained. The step cut displays the color of benitoite to advantage, with only slight loss of brilliancy. Its chemical composition is BaTi(Si3O9). The pleochroism of benitoite is pale to dark-blue or purplish and colorless.  The only location where gem-quality material has been found is in San Benito County, Califor… At the top, you’ll find medium-dark stones. The same rock was encountered in the crosscut tunnel 40 feet below the surface and 30 feet north of the main tunnel. It is a rare mineral found in very few areas, including California, San Benito County, Japan and Arkansas. Some crystals of benitoite appear red to dark maroon due to inclusions of minute neptunite crystals. It has a rare twinned crystal shape of 5 points, and an even rarer twinned crystal shape of 6 points, “David’s star,” with precisely 24 known specimens making it more precious than diamonds. Jointing of the rock and the irregular nature of the vein, however, make accurate measurements difficult. The elevation of the mine is about 4,800 feet above sea level; the elevation of Santa Rita Peak is 5,161 feet. The common forms observed are the base c(0001), trigonal
These schists may be micaceous or more basic, having common hornblende, actinolite, or glaucophane as characteristic minerals. Benitoite, a barium titanium silicate, can occur in rich blue crystals that are as striking and flawless as the finest sapphires. Neither benitoite nor neptunite have been found associated with this natrolite. Benitoite is usually found in a matrix of three other minerals—natrolite, hard blue schist, and cement-like crossite. The incline shaft was sunk 35 feet deep from the north side of the open cut at about the middle. Kay Robertson Collection Here is a beautiful crystal of the Zeolite Group species, Natrolite. Fluorescent benitoite: This is a photograph of small benitoite crystals under ultraviolet light. Deeper colored stones may be cut in the same way or with the table in an intermediate position, if the color is very strong. Very light and very dark rocks lie at the lower end of the price continuum. This occurs in low temperature, high-pressure conditions typical of subduction zones at the edge of the converging plate. This gem is quite expensive Rich blue, clean stones at a carat and above sizes will command high prices. The neptunite is subject to the same relations with the natrolite and is, in places, partly surrounded by benitoite. An excellent and uncommon, fairly large crystal for the locale. Hardness: is 6 – 6.5 Whether he discovered it while out alone or on a second trip with L. B. Hawkins, of Los Angeles, is a point in dispute. Specimens cut by Mr. Eacret were thought to be sapphire. Other rare gems and minerals include Neptunite, Joaquinite, djurleite, and Natrolite. After 100 years, the Benitoite Gem Mine is finally open and offering field trips to the public. The size of the gems cut from benitoite range in weight from a small fraction of a carat to several carats. 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