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Spiky Colemanite Aggregate
BORATES; HYDROUS BORATES · MONOCLINIC

Colemanite

Ca2B6O11 · 5H2O

Hardness
4–4.5
Streak
White
Spec. Gravity
2.4
System
Monoclinic

About

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.

Crystal Forms & Aggregates

Other ID Marks

Complex Tests

May develop dust on certain crystal faces due to a pyroelectric charge.

Striking Features

Environment

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

Distinguishing Similar Minerals

Photos

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Crystal forms

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Complex Short Prismatic
Short Prismatic