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Colemanite
Current inventory:  1 gem
 

Chemistry:  Ca₂B₆O₁₁·5(H₂O)

Discovered in 1884;   IMA status: Valid (pre-IMA; Grandfathered).
Colemanite is named in honor of William Tell Coleman (1824–1893), owner of the Death Valley, California mine where the mineral was first found and pioneer developer of the borax industry in California, USA.

Classification

Mineral Classification:

Borates

Strunz 8th Ed. ID:

5/J.03-10

Nickel-Strunz 10th Ed. ID:

6.CB.10

6 : BORATES
C : Triborates
B : Ino-triborates

Related to:

Colemanite-Hydroboracite Series

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

As equant to short prismatic crystals, with large and multiple terminating forms, to 30 cm; pseudorhombohedral and pseudo-octahedral; nearly 50 forms measured; cleavable massive, granular, most commonly nodular.

Twinning:

None

Physical Properties

Cleavage:

[010] Perfect, [001] Distinct

Fracture:

Irregular, Uneven, Sub-Conchoidal

Tenacity:

Brittle

Moh's Hardness:

4.5

Density:

2.422 (g/cm³)

Luminescence:

May fluoresce and phosphoresce strong yellowish white or greenish white in SW UV.

Radioactivity:

Not Radioactive

Other:

Very slightly soluble in water (1 part in 1,100 at 20°-25°)

Optical Properties

Color:

Colorless, Gray, Gray white, Yellowish white, White

Transparency:

Transparent to Translucent

Luster:

Vitreous to Adamantine

Refractive Index:

1.586 - 1.614  Biaxial ( + )

Birefringence:

0.0280

Dispersion:

Weak; r > v

Pleochroism:

None

Occurances

Geological Setting:

A common constituent in borate deposits formed in arid alkaline lacustrine environments, deficient in sodium and carbonate, typically under warm conditions.

Common Associations:

Calcite, Celestine, Ginorite, Gowerite, Gypsum, Howlite, Kernite, Lüneburgite, Nobleite, Priceite, Searlesite, Ulexite

Type Locality:

Furnace Creek District, Death Valley, Inyo Co., California, USA

Year Discovered:

1884

View mineral photos:

Colemanite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Colemanite is an extremely rare gem that is not particularly attractive but is a rarity for collectors. Gems are very difficult to facet since they are brittle and fragile with perfect cleavage in one direction. Current sources of Colemanite are Yermo, Boron, Death Valley and other California localities, USA; Chile; and Panderma, Turkey.
 

  
Colemanite gems for sale: