COLEMANITE: Boron, California (26.50)
Colemanite is cut only as a curiosity, since it has no attractive colors. Faceted gems are normally colorless, have a low dispersion (no fire) and are brittle and fragile as well as difficult to cut. They have no appeal except to collectors of the unusual, and material for cutting is potentially abundantly available, since transparent material is not extremely rare.
Colemanite Value
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Colemanite Information
| Data | Value |
| Name | Colemanite |
| Crystallography | Monoclinic. Crystals are equant, prismatic, pseudorhombohedral; massive, cleavable; granular, and as aggregates. |
| Colors | Colorless, white, grayish, yellowish white. |
| Luster | Vitreous to adamantine. |
| Hardness | 4.5 |
| Density | 2.42 |
| Birefringence | 0.028 |
| Cleavage | Perfect 1 direction. Fracture subconchoidal to uneven. Brittle. |
| Stone Sizes | Could be as much as 50-100 carats from large crystals or masses. Crystals are normally up to about 1 inch in size. Smithsonian Institution (Washington, D.C): 14.9 (California). |
| Luminescence | May fluoresce and phosphoresce strong yellowish white or greenish white in SW. |
| Spectral | Not diagnostic |
| Formula | Ca2B6O11 · 5H2O. |
| Pleochroism | None |
Optics: a = 1.586; β = 1.592; γ= 1.614.
Biaxial (+), 2V ~55°.
Occurrence: In saline lake deposits in arid regions.
Widespread at localities in California, especially Boron and Death Valley.
Argentina; USSR; Turkey.
Comments: Colemanite is cut only as a curiosity, since it has no attractive colors. Faceted gems are normally colorless, have a low dispersion (no fire) and are brittle and fragile as well as difficult to cut. They have no appeal except to collectors of the unusual, and material for cutting is potentially abundantly available, since transparent material is not extremely rare.
Name: After William T. Coleman, owner of the mine where the mineral was first found
 | An Introduction To Turkey’s Gemstones |
