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. |
| Crystallographic Forms | |
| 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. |
| Optic Sign | Biaxial +, Biaxial - |
Danburites: Charcas, Mexico (8.5, crystal ~ 2 1⁄2 inches long). Photo © Joel E. Arem, PhD, FGA. Used with permission.
With poor cleavage and a hardness of 7, danburite can withstand the rigors of all jewelry applications, including rings and bracelets. It has good resistance to damage from accidental blows and scratches. In terms of toughness and wearability, it ranks with popular jewelry stones like quartz and topaz.
18k white gold ring with danburite and diamonds. Photo courtesy of liveauctioneers.com and Don Presley Auction.
Danburite’s colors typically range from colorless to light yellow, pale pink, or tan.
Although a modest dispersion means cut danburites won’t show colorful flashes, properly cut gems can still look 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.
Most danburites show a sky-blue fluorescence in longwave ultraviolet light and a red phosphorescence when heated. However, some specimens from Sri Lanka and Tanzania show no luminescence at all.
Laboratories have synthesized danburite for research into phosphorescence. However, there’s no known jewelry use for this material.
Typically, danburites receive no enhancements, but some Russian specimens have undergone a stable radiation treatment for color enhancement.
Irradiated, square radiant-cut danburites, 5.76 ctw, 8.1 mm, Dal’Negorsk, Russia. © The Gem Trader. Used with permission.
First discovered in Danbury, Connecticut, gem-quality danburite has since been found in many locations all over the world. Notable sources include the following:
Golden yellow danburite, 32.97 cts, 20.93 x 16.25 mm, custom Barion emerald cut, Madagascar. © Kosnar Gem Co. Used with permission.
Danburite, Merelani Hills, Arusha Region, Tanzania. © Rob Lavinsky, www.iRocks.com. 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.
Due to some heat sensitivity, avoid steam cleaning this gem. Otherwise, danburite requires no special care. Consult our gemstone jewelry cleaning guide for more care recommendations.
Round brilliant-cut danburite, 1.18 cts, 6.9 mm, Obira Mine, Oita Prefecture, Japan. © The Gem Trader. Used with permission.
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