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Spiky Colemanite Aggregate

The Mineral colemanite




Colemanite forms in evaporite deposits together with other borates, and is one of the more stable of borate minerals. It 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, as no satisfactory explanation has been given to how Colemanite is pyroelectric. 

Colemanite was named after William T. Coleman, a mine owner who lived in San Francisco.
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
In large and well-formed bipyramidal and prismatic crystals. Crystals may also be platy, and may be in grainy aggregates. Also 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 Often fluorescent 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 AUCTIONS



USES
Colemanite has many important uses. It is a significant ore of boron, and was the most important ore prior to the discovery of Kernite 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 collector mineral.

NOTEWORTHY LOCALITIES
Some of the largest deposits of Colemanite are in the 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 Colemanite deposits are Boron, in the Kramer District, Kern Co.; Tick Canyon, Lang, Los Angeles Co; and the Boraxo Mine, Inyo Co. In Nevada, it comes from the Muddy Mountains, Clark Co.

Colemanite 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.

COMMON MINERAL ASSOCIATIONS
Ulexite, Borax, Realgar, Celestine

DISTINGUISHING SIMILAR MINERALS
Celestine - Lower hardness, higher specific gravity.
Calcite - Lower hardness, has perfect rhombohedral cleavage.
Datolite - Different mode of occurrence.


colemanite PHOTOS
 
ADDITIONAL RESOURCES
 
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