Yellow cushion-cut danburite, 6.53 cts, 12.0 x 9.7 x 8.6 mm, Myanmar. © ARK Rare Gems. Used with permission.
A very durable gemstone, danburite is an excellent choice for jewelry use. Although the mineral isn’t rare, large facetable pieces are scarce. Still, sufficient material exists for gem enthusiasts and adventurous jewelry lovers to add this lovely and underappreciated stone to their collections.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
Tried and true gem value factors apply to danburite. All other things being equal, larger, cleaner, better cut and better colored stones have a higher value per carat. However, a truly colorless specimen would surpass a very pale yellow or slightly pink stone in value per carat.
Princess-cut colorless 8.65-ct danburite, 12.26 mm, Russia. © Kosnar Gem Co. Used with permission.
| Data | Value |
|---|---|
| Name | Danburite |
| Crystallography | Orthorhombic; Crystals prismatic with wedge-shaped terminations, like topaz. |
| Refractive Index | 1.627 - 1.641 |
| Colors | Colorless, white, pink, light to dark yellow, yellowish brown, brown, blue. |
| Luster | Vitreous to greasy. |
| Hardness | 7 |
| Wearability | Excellent |
| Fracture | Subconchoidal to uneven |
| Specific Gravity | 2.97-3.03, usually 3.00. |
| Birefringence | 0.008-0.009 |
| Cleavage | Indistinct |
| Dispersion | 0.017 |
| Luminescence | Sky blue to bright blue-green in LW. Also, thermoluminescent (red). |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, Phosphorescent, UV-Long |
| Transparency | Transparent. |
| Absorption Spectrum | Sometimes shows rare earth spectrum, so-called didymium lines. |
| Phenomena | Chatoyancy (rare). |
| Formula | CaB2Si2O8 |
| Pleochroism | Weak: pale-yellow/yellow. |
| Optics | a = 1.627-1.633; β = 1.633-1.637; γ = 1.636-1.641. Biaxial (-); 2V= 88° in red to green light; optically (+) at lower wavelengths. |
| Etymology | After the type locality, Danbury, Connecticut. |
| Occurrence | In dolomites; in carbonate veins in granitic rocks. |
| Inclusions | Fingerprints (healed fractures), hollow growth tubes. |
Danburite: Charcas, Mexico (8.5, crystal ~ 2 1⁄2 inches long). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Danburite’s colors typically range from colorless to light yellow, pale pink, or tan. With poor cleavage and a hardness of 7, it ranks with popular jewelry stones such as quartz and topaz in toughness. Although its modest dispersion means cut danburites lack fire, properly cut gems are very bright. Rare specimens may also display chatoyancy.
This danburite shows an unusual color, dark blue, as well as a rare chatoyant “cat’s eye” effect. Round cabochon, 0.73 cts, 5.1 mm, Alto Chapare District, Cochabamba Dept., Bolivia. © The Gem Trader. Used with permission.
Interestingly, most specimens fluoresce a sky blue color in longwave ultraviolet light and phosphoresce red when heated.
Laboratories have synthesized danburite for research into phosphorescence. However, there’s no known jewelry use for this material.
No known gem treatments.
Danburite mass with crude crystal faces, Danbury, Fairfield Co., Connecticut, USA. © Rob Lavinsky, www.iRocks.com. Used with permission.
First discovered in Danbury, Connecticut, gem-quality danburite has since been found in many locations. Other notable sources include the following:
Golden yellow danburite, 32.97 cts, 20.93 x 16.25 mm, 32.97 cts, custom Barion emerald cut, Madagascar. © Kosnar Gem Co. Used with permission.
Danburites, especially colorless material from Mexico, typically range in size between 1 and 5 carats. Yellow gems from Myanmar between 7 and 10 carats are very rare.
Danburite, Merelani Hills, Arusha Region, Tanzania. © Rob Lavinsky, www.iRocks.com. Used with permission.
Due to some heat sensitivity, avoid steam cleaning this gem. Otherwise, danburite requires no special care. You can use these gems for all jewelry applications, including rings and bracelets. Consult our gemstone jewelry cleaning guide for more care recommendations.
Cut Danburite, Locality: Anjanabonoina, Ikaka, Ambohimanambola Commune, Betafo District, Vakinankaratra Region Antananarivo Province, Madagascar (0.47 cts). Photo by Didier Descouens. Licensed under CC By-SA 4.0.
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