Online Encyclopedia

COLEMANITE

Online Encyclopedia
Originally appearing in Volume V06, Page 666 of the 1911 Encyclopedia Britannica.
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COLEMANITE  , a hydrous

calcium borate, Ca2B6O11+5H2O, found in California as brilliant ,
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monoclinic crystals . It contains 50.9% of boron trioxide, and is an important source of commercial borates and boracic acid . Beautifully
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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
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plane of symmetry of the crystals . Hardness 4-4i; specific gravity 2.42 . The
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mineral was first discovered in 1882 in
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Death Valley, Inyo county, California, and in the following
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year it was found in greater abundance near Daggett in
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San Bernardino county, forming with other borates and borosilicates a bed in sedimentary strata of sandstones and clays; in more
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recent years very large masses have been found and worked in these localities, and also in Los Angeles county (see
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Special Report, 1905, of U.S . Census Bureau on Mines and Quarries; and Mineral Resources of the U.S., 1907) . . 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
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species . They are massive white minerals, the former friable and
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chalk-like, and the latter
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firm and compact in texture . Priceite occurs near Chetco in
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Curry county,
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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
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size from that of a
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pea to masses weighing 2001b . Pandermite comes from
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Asia Minor, and is shipped from the
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port of Panderma on the Sea of Marmora: it occurs as large nodules, up to a ton in
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weight, beneath a thick bed of
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gypsum . Another borate of commercial importance found abundantly in the Californian deposits is ulexite, also known as boronatrocalcite or " cotton-ball," a hydrous calcium and sodium borate, CaNaB5O9+8H20, which forms rounded masses consisting of a loose aggregate of
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fine fibres .

It is the

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principal species in the borate deposits in the Atacama region of South
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America . (L . J .

End of Article: COLEMANITE
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