Benitoite
The rare mineral benitoite is a ring silicate having the chemical composition BaTi [ Si3O9 ]. It crystallizes in the hexagonal crystal system and developed predominantly trigonal and / or hexagonal, prismatic to tabular crystals in most pyramidal sapphire blue color.
Benitoite be processed solely for gemstones.
Special Features
The sapphire blue ( with a hint of violet ) of the Benitoits ( sometimes referred to as " blue diamond " ) may be caused by traces of iron. Very rarely will you also clear, white, green, gray, pink to purple, orange, red or maroon crystals ( with inclusions of other minerals such as Neptunite ). Benitoite has a higher birefringence than diamond. Because of its strong dichroism benitoite shows either no color or blue or purple. Under short-wave UV light Benitoite fluoresces light blue under long wave UV light show some crystals have a reddish color. The dispersion (different refraction of light depending on the wavelength of the incident light ) of benitoite can cause a sparkle of red and green flashes.
The mineral is hard enough ( Mohs hardness 6.5 ) to be processed as a gemstone, but it is still pretty unknown. Faceted Benitoite weigh usually less than 1 ct. A faceted, clear benitoite with a good color, weighs more than 0.5 ct is rare and expensive.
Etymology and history
The first discovery of Benitoite in February 1907 made by the prospector James M. couch. He searched on behalf of Roderick W. Dallas in the Diablo Mountains to cinnabar or copper. Set on the hillside entered couch a man-sized cavity between two crevices and looked at the floor countless blue, herausgewitterte of white Natrolite crystals of Benitoite. Some pieces were sent to the faceting to a jeweler in San Francisco. Finally, George Davis Louderback, professor of geology at the University of California at Berkeley, charged with the identification of the unknown crystals. He recognized the new mineral, described it in the same year in detail and named it after its type locality San Benito County benitoite.
For the degradation of the "Dallas Mining Company " was founded and built a camp. The following preserved only about 1 % of the Benitoite in the degradation of the use of dynamite to make work easier. 1912, the mine was closed because Dallas assumed that she was exhausted. After a brief reopening in 1933 the mine was leased to various entrepreneurs. 1967 leased as Grey and B. Forrest mine. The two bought the mine in 1987 and extended it, the name was changed to " Benitoite Gem Mine ." In 1997 the mine was leased to the Company AZCO that no significant amounts of Benitoite was despite major investments. Collector's Edge Minerals, Inc. bought the mine in 2000. 2005, the Company sold the mine in 2005 to Dave Schreiner. Dave is contractually obligated to use heavy machinery until 2015. It allows visitors to dig for a charge on the mine site.
Benitoite was selected in 1985 as the official "State Gemstone " of the State of California.
Classification
In the old ( 8th edition ) and new classification of minerals ( 9th Edition ) by Strunz heard the benitoite to the Department of " ring silicates ( cyclo- silicates) ." This division is further divided, however since the new Strunz'schen Mineral classification and according to its crystal structure, the mineral now part of the subdivision of the " ring silicates with [ Si3O9 ] 6 - three - Simple rings without insular complex anions ".
The classification of minerals according to Dana assigns the benitoite in the department " Cyclosilicates cyclosilicates Three- Membered Rings anhydrous, no other anion " (Translated: Anhydrous ring silicates with triple rings without other anions ), where he claimed together with Bazirit, Pabstit and Wadeit the his name benitoite group forms with the number 59.01.01.
Education and Locations
Benitoitkristalle be formed in hydrothermal solutions in natrolite veins that contained relatively high proportions of hydrothermal solutions for unusual elements such as barium, titanium, fluorine, iron, and others. Benitoite usually occurs together with albite, Joaquinite, Neptunite and serpentine. Natrolite, which came into being last in the mineral Benitoite deposits, usually covers the Benitoite crystals, which is why it eg must be removed with hydrochloric acid to make the Benitoite crystals visible.
Benitoite come almost exclusively from the rich mineralized (more than 150 semi-precious stones and gems ) Serpentinkörper of the New Idria Mine area near the San Benito River in San Benito County, California (USA). There you can benitoite at the southern end of the " Diablo Range" find a mountain belt, the basalt, chert, greywacke, shale, serpentinite and Cretaceous as well as tertiary sandstones contains.
The best known because of its valuable crystals Benitoite Mine is the " Benitoite Gem Mine" (also known as " Benitoite Mine" and "Dallas Gem Mine "), which is owned by Dave Schreiner ( from Coalinga, California). Dave allows visitors to dig for a fee in the mine area.
Within a radius of 10 km around the " Benitoite Gem Mine" there are four other benitoite mines in Clear Creek: The " Junnila Mine", about 8 km northwest of the " Benitoite Gem Mine ," the " Numero Uno Mine " the " Victor Mine" and the " Santa Rita peak Property ". In addition to the excavation site in San Benito County can be found less valuable benitoite in Arkansas ( " Diamond Jo Quarry " at Magnet Cove in Hot Spring County), " Big Creek " ( in Fresno County in the Sierra Nevada in California ), Japan ( Ohmi at Itoigawa in Niigata Prefecture, Chubu region on Honshu ), and finally in Broken Hill ( New South Wales, Australia).
Crystal structure
Benitoite crystallizes in the hexagonal crystal system in the space group with the lattice parameters a = 6.641 Å and c = 9.759 Å and two formula units per unit cell.
Use as a gemstone
Large, ground Benitoite (over 1 carat ) are very rare. Usually they show a deep, intense blue. Clear crystals of good quality can be sanded to gemstones and can certainly withstand the comparison with the sapphire. Likelihood of confusion with other precious stones such as cordierite, spinel, tanzanite, blue or pink varieties of tourmaline and zircon. For Benitoite are no treatments or "improvements" known.
Similar to sapphire, ruby or other known gems are great, pure, Benitoite with a good blue very expensive. Stones with a very light or very dark blue are less valuable. Unlike other gemstones the cut of a Benitoite is less important because you are trying during grinding to get as much material as possible.