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Encyclopedia Britannica - Main :: CLI-COM |
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COLEMANITE , a hydrous calcium borate, Ca2B6O11+5H2O, found in California as brilliant ,monoclinic crystals. It contains 50.9% of boron trioxide, and is an important source of commercial borates and boracic acid. Beautifully developed crystals, up to 2 or 3 in. in length, encrust cavities in compact, white colemanite; they are colourless and transparent, and the brilliant lustre of their faces is vitreous to adamantine in character. There is a perfect cleavage parallel to the plane of symmetry of the crystals. Hardness 4-4i; specific gravity 2.42. The mineral
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Priceite and pandermite are hydrous calcium borates with very nearly the same composition as colemanite, and they may really be only impure forms of this species. They are massive white minerals, the former friable and chalk-like, and the latter firm and compact in texture. Priceite occurs near Chetco in Curry county, Oregon, where it forms layers between a bed of slate and one of tough blue steatite; embedded in the steatite are rounded masses of priceite varying in size from that of a pea to masses weighing 2001b. Pandermite comes from Asia Minor , and is shipped from the port of Panderma on the Sea of Marmora: it occurs as large nodules, up to a ton in weight
Another borate of commercial importance found abundantly in the Californian deposits is ulexite, also known as boronatrocalcite or " cotton
South
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