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Spiky Colemanite Aggregate

The Mineral colemanite

Colemanite was named after William T. Coleman, a mine owner who lived in San Francisco. Colemanite forms in evaporite deposits together with other borates. It is one of the more stable of borate minerals. 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.
Chemical Formula Ca2B6O11 · 5H2O
Composition Hydrous calcium borate
Color Colorless to white, yellow, brown
Streak White
Hardness 4 - 4.5
Crystal System Monoclinic
3D Crystal Atlas
(Click for animated model) 
Crystal Forms
and Aggregates
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, as spiky aggregates, and in drusy linings of geodes.
Transparency Transparent to translucent
Specific Gravity 2.4
Luster Vitreous to adamantine
Cleavage 1,1 ; 3,1
Fracture Uneven
Tenacity Brittle
Other ID Marks Usually fluoresces a pale white in shortwave ultraviolet light.
Complex Tests May develop dust on certain crystal faces due to a pyroelectric charge.
In Group Borates; Hydrous Borates
Striking Features Crystal shape, hardness, cleavage, and occurrences
Environment Borax evaporite deposits in dry lakes of arid regions.
Rock Type Sedimentary
Popularity (1-4) 2
Prevalence (1-3) 2
Demand (1-3) 1

Colemanite ON EBAY

Colemanite has many important uses. It is a significant ore of boron, and 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 cosmetic uses. It is a popular collectors mineral.

Some of the largest deposits of this mineral are in the southwestern U.S. Very large 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, in the Kramer District, Kern Co.; Tick Canyon, Lang, Los Angeles Co; and the Boraxo Mine, Inyo Co. Colemanite also comes from Nevada in the Muddy Mountains, Clark Co.

Localities outside the U.S. include Bigadic, Marmara Region, Turkey; the dry lake deposits in the Atacama Desert of Chile; Salinas Grandes, Argentina; and the Indebor Deposit, Kazakhstan.

Ulexite, Borax, Realgar, Celestine

Celestine - Softer (3 - 3½), heavier (3.9 - 4.0).
Calcite - Softer (3), has perfect rhombohedral cleavage.

colemanite PHOTOS
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