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A major source of boron, colemanite was discovered in 1884 and named for the California mine owner where it was first found, William Tell Coleman. The color of this stone ranges from colorless to white to grey, sometimes yellowish. Specimens are very sensitive to heat. The short, prismatic crystals are often sought after by collectors and colemanite is rarely seen in the form of gemstones as it presents a challenge to lapidaries as crystals are soft, brittle and have perfect cleavage.

Colemanite Rough
Colemanite Classification
Common Name Colemanite
Species Colemanite
Colemanite Optical Properties
Transparency Transparent - Translucent
Dispersion Strength: Weak Fire
Refractive Index 1.586-1.615
Birefringence 0.028- 0.030
Optic Character Biaxial
Optic Sign Positive
Polariscope Reaction Doubly Refractive (DR)
Pleochroism None
Colemanite Characteristic Physical Properties
Hardness 4-4.5
Streak White
Specific Gravity 2.400-2.420
Toughness Poor
Luster Vitreous
Fracture Uneven
Cleavage Perfect, in one direction
Colemanite Chemistry & Crystallography
Chemical Name hydrated calcium borate
Chemical Formula Ca2B6O11.5H2O
Crystal System Monoclinic
Chemistry Classification Borate

Colemanite Colors

  • Yellow Colemanite Yellow
  • Colorless Colemanite Colorless
  • White Colemanite White
  • Gray Colemanite Gray

Countries of Origin

United States of America (the)

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Tim Matthews


Tim Matthews

Tim Matthews is President and Chief Executive Officer of Jewelry Television® (JTV), as well as a member of the company's Board of Directors. He oversees and leads all aspects of the company's powerful omni-digital retail platform that uniquely specializes in fine jewelry and gemstones. His passion for business and gemstones has led him to become a recognized expert in the field of gemology. He is a life member of the Gemmological Association of Great Britain (Gem-A) and has earned Gem-A's highest degrees, the Gemmology (FGA) and Diamond (DGA) diplomas. He is also a Graduate Gemologist (GG) of the Gemological Institute of America (GIA) and has also completed GIA's Graduate Diplomas in Diamonds, Colored Stones and Pearls. Under his leadership, JTV has become the leader in the sourcing and selling of color gemstones and jewelry.

This page was created on June 27, 2014.

This page was last edited on October 24, 2019.