Colemanite
Current inventory:  1 gem
 

  
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.

Discovered in 1884; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Ca₂B₆O₁₁ · 5(H₂O)

Hydrated Calcium Borate

Molecular Weight:

411.09 gm

Composition:

Calcium

19.50 %

Ca

27.28 %

CaO

Boron

15.78 %

B

50.81 %

B₂O₃

Hydrogen

2.45 %

H

21.91 %

H₂O

Oxygen

62.27 %

O

100.00 %

100.00 %

= TOTAL OXIDE

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.

Varieties:

None

Synonyms:

Borspar, Neocolemanite

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:

Perfect on [010], Distinct on [001]

Fracture:

Irregular/Uneven to Sub-Conchoidal

Tenacity:

Brittle

Moh's Hardness:

4.5

Density:

2.423 (g/cm³)

Luminescence:

Fluorescent; bright pale yellow under SW UV and LW UV. May phosphoresce pale green.

Radioactivity:

Not Radioactive

Other:

Pyroelectric and Piezoelectric at very low temperatures. 
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:

Relatively 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

Common Impurities:

None

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 a rare gem that is not particularly attractive but is a rarity for collectors. Colemanite is an interesting gem in that it is pyroelectric and piezoelectric at very low temperatures. Colemanite is also fluorescent showing bright pale yellow under shortwave and longwave UV and may phosphoresce pale green. Gems are very difficult to facet since Colemanite is brittle and fragile with perfect cleavage in one direction and it is very slightly soluble in water.

Colemanite is a complex borate mineral, and like other borates, it is found in playa lakes and other evaporite deposits. Colemanite is an ore of boron and a source of borax which is a cleaning agent and useful industrial chemical.

Current sources of Colemanite are Yermo, Boron, Death Valley and other California localities, USA; Chile; and Panderma, Turkey.
 

  
Colemanite gems for sale: