Colemanite Value, Price, and Jewelry Information

Colorless, round brilliant colemanite, 0.39 cts, 5 mm, Billie Mine, Boron, California. © The Gem Trader. Used with permission.

Colemanite

Colemanite is an abundant mineral, and transparent material isn’t rare. However, gem cutters rarely facet these typically pale stones. Difficult to cut and wear, colemanites are better suited for collectors of unusual gemstones.

Colemanite Information

Data Value
Name Colemanite
Colors Colorless, white, grayish, yellowish white, light amber-orange, brown.
Crystallography Monoclinic. Crystals are equant, prismatic, pseudorhombohedral; massive, cleavable; granular, and as aggregates.
Refractive Index 1.586-1.614
Luster Vitreous to adamantine.
Hardness 4.5
Fracture Subconchoidal to uneven.
Specific Gravity 2.42
Birefringence 0.028
Cleavage Perfect 1 direction.
Dispersion Weak.
Heat Sensitivity Very heat sensitive.
Luminescence May fluoresce and phosphoresce strong yellowish white or greenish white.
Luminescence Present Yes
Luminescence Type Fluorescent, Phosphorescent
Transparency Translucent to transparent.
Absorption Spectrum Not diagnostic.
Formula

Ca2B6O11 · 5H2O.

Pleochroism

None.

Optics

a = 1.586; β = 1.592; γ = 1.614. Biaxial (+), 2V  ~ 55°.

Optic Sign Biaxial +
Etymology

After William T. Coleman, owner of the mine where the mineral was first found.

Occurrence

In saline lake deposits in arid regions.

Colemanite - 26.50 cts

Colemanite: Boron, California (26.50). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Comments

Colemanite serves as an ore for boron and has many industrial uses. As a gemstone, however, it has weak dispersion, so it shows little fire, and normally occurs colorless. Since it also has perfect cleavage and a hardness of only 4.5, this fragile gem would make an unlikely choice for a jewelry stone.

Identifying Characteristics

Colemanites are both pyroelectric and piezoelectric.

Since colemanite is rarely faceted, its birefringent facet doubling is rarely seen. This large, eye-clean, custom shield-cut specimen displays the effect very nicely. 9.33 cts, 14 x 12.1 mm, Boron, California. © The Gem Trader. Used with permission.

Synthetics

Scientists have synthesized colemanites for a variety of research projects, including studies of their electrical properties. However, there’s no known jewelry use for this lab-created material.

Enhancements

No known gemstone treatments.

Sources

The southwestern United States, particularly Boron and Death Valley, California, produces beautiful colemanite crystals. Other notable sources include Argentina, Kazakhstan, and Turkey.

colemanite crystals - Turkey

This crystal specimen contains gemmy, honey brown colemanites with “second generation” colorless colemanites on their edges. 5.4 x 5.0 x 3.7 cm, Kestelek Mine, Mustafa Kemalpafla, Bursa Province, Marmara Region, Turkey. © Rob Lavinsky, www.iRocks.com. Used with permission.

Stone Sizes

Large crystals and masses could yield gems of 50-100 carats. Crystals normally range up to about 1 inch in size.

  • Smithsonian Institution (Washington, DC): 14.9 (California).

Care

Colemanites have considerable heat sensitivity, so any setting in metal jewelry should be done very carefully. If worn as jewelry, they require protective settings. These gems are also slightly soluble in water. Don’t soak these gems during cleaning and make sure they’re dry before storing. Clean them only with a soft brush, mild detergent, and warm water. For more care recommendations, consult our gemstone jewelry cleaning guide.

colemanite rough and cut set - California

This rough and cut set features a cluster of tabular colemanite crystals and a faceted, 2.47-ct, 8 mm colemanite. Boron, Kramer District, Kern Co., California, USA. © Rob Lavinsky, www.iRocks.com. Used with permission.