Colemanite

Colemanite is named after William Tell Coleman, mine owner and a founder of the California borax industry.

Colemanite has variable crystal habits: short prismatic crystals, stubby and bead-like equant crystals, flattened crystals, that appear bladed with terminations.

Colemanite is highly sensitive to heat.

Colemanite Gemstones by Colour

This table shows the variety of hues this gemstone can be found in. Click on a photo for more information.
 

Colemanite Gemstones by Size

This table shows distribution of Colemanite gemstone sizes that are listed on this site. This can give a good indication as to the general availability of this gemstone in different sizes.
Contributed photos
Lightest:0.87 cts
Heaviest:9.33 cts
Average:4.08 cts
Total photos:3
Do you have a larger Colemanite? Why not upload a photo?
0.87ct to 1.72ct1.72ct to 2.56ct2.56ct to 3.41ct3.41ct to 4.25ct4.25ct to 5.10ct5.10ct to 5.95ct5.95ct to 6.79ct6.79ct to 7.64ct7.64ct to 8.48ct8.48ct to 9.33ct
General Information
Chemical Formula
Ca
 
2
B
 
6
O
 
11
· 5H
 
2
O
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Photos of natural/un-cut material from mindat.org
Physical Properties of Colemanite
Mohs Hardness4.5
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Specific Gravity2.40 to 2.42
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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TenacityBrittle
Michael O’Donoghue, Gems, Sixth Edition (2006)
Cleavage QualityPerfect
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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FractureUneven
Arthur Thomas, Gemstones (2009)
Heat SensitivityHighly sensitive
Arthur Thomas, Gemstones (2009)
Optical Properties of Colemanite
Refractive Index1.584 to 1.615
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Optical CharacterBiaxial/+
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Birefringence0.028 to 0.030
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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PleochroismNil
Arthur Thomas, Gemstones (2009)
DispersionRelatively weak
Arthur Thomas, Gemstones (2009)
Colour
Colour (General)Colourless, gray-white
Walter Schumann, Gemstones of the world (2001)
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TransparencyTransparent,Translucent
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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LustreVitreous
Arthur Thomas, Gemstones (2009)
Fluorescence & other light emissions
Fluorescence (General)Commonly white or green
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Crystallography of Colemanite
Crystal SystemMonoclinic
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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HabitEquant to short-prismatic crystals
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Geological Environment
Where found:Colemanite is a common constituent of borate deposits formed in sodium- and carbonate-poor lake environments.
Michael O’Donoghue, Gems, Sixth Edition (2006)
Further Information
Mineral information:Colemanite information at mindat.org
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