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Chemical Formula | Ca2B6O11 · 5H2O | ||
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Composition | Hydrous calcium borate | ||
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Color | Colorless to white, sometimes yellowish or brownish from impurities | ||
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Streak | White | ||
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Hardness | 4 - 4½ | ||
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Crystal Forms and Aggregates |
(Monoclinic) Occurs in large and well-formed bipyramidal and prismatic crystals. Crystals may also be platy, and can occur in grainy aggregates. Also occurs as groups of thin, long, bipyramidal crystals, massive, and in drusy linings of geodes. | ||
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Transparency | Transparent to translucent | ||
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Specific Gravity | 2.4 | ||
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Luster | Vitreous | ||
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Cleavage | 1,1 ; 3,1 | ||
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Fracture | Uneven | ||
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Tenacity | Brittle | ||
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Other ID Marks | May fluoresce pale white in shortwave ultraviolet light | ||
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In Group | Borates ; Hydrous borates | ||
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All About | Colemanite forms in evaporite deposits together with other borates. Colemanite is pyroelectric and develops an electrical charge
during a change of temperature. The crystal symmetry of prismatic monoclinic minerals would scientifically disqualify
them from being pyroelectric, since pyroelectricity is
directly related to crystal symmetry. This mineral is
therefore regarded as a scientific oddity, and as of yet
no explanation has been given to how Colemanite is
pyroelectric. Colemanite was named after William T. Coleman, a mine owner who lived in San Francisco. |
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Uses | Colemanite has many important uses. It is one of the most significant ores of boron, and actually was the most important ore before Kernite was discovered in 1926. It is also used in the manufacture of heat resistant glass, and has other industrial, medicinal, and cosmetical uses. | ||
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Striking Features | Crystal shape, hardness, cleavage, and occurrences | ||
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Complex Tests | May develop dust on certain crystal faces due to a pyroelectric charge. | ||
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Popularity (1-4) | 2 | ||
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Prevalence (1-3) | 2 | ||
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Demand (1-3) | 1 | ||
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Distinguishing Similar Minerals |
Celestine - softer (3 - 3½), heavier (3.9 -
4.0) Calcite - softer (3), has perfect rhombohedral cleavage |
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Commonly Occurs With |
Ulexite, Borax, Realgar, Celestine | ||
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Noteworthy Localities |
The largest deposits of this mineral are in
the southwestern U.S. Some of the largest crystals come
from Death Valley, Inyo Co., California. Crystal-filled nodules associated with Celestine were found in the Calico district in San
Bernardino Co., California. Other California occurrences
are Boron, Kern Co.; Lang, Los Angeles Co; and Frazier
Mountain, Ventura Co. Colemanite also comes from the
Muddy Mountains, Clark Co., Nevada. Localities outside the U.S. include the Atacama Desert of Chile; Salinas Grandes, Argentina; Bigadic, Turkey; and the Indebor Deposit, Kazakhstan. |
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Picture Icon Links |
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Picture Links | 1. Grainy crystal aggregate |
