DIASPORE: Turkey (2.10). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Diaspore is hard enough to make a durable jewelry stone, but the typical light brownish color is not easy to sell. Despite the large Turkish material, this is a very rare gemstone indeed.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
| Data | Value |
|---|---|
| Name | Diaspore |
| Varieties | Color Change Diaspore |
| Colors | Colorless, white, yellowish, pink, rose red to dark red (due to Mn), lilac, greenish, brownish. |
| Hardness | 6.5 - 7 |
| Fracture | Conchoidal |
| Cleavage | Perfect 1 direction |
| Stone Sizes | Diaspore crystals from Massachusetts were, when found, apparently suitable for cutting, and a few gems may have been cut from the Pennsylvania material. However, cut disapore was, at best, an extremely unlikely gemstone until the find of crystals in Turkey. This locality has produced the vast majority of cut diaspore now in existence. Moreover, the locality produced cuttable pieces enormously larger than had ever been known previously in the mineral. Private Collection: some of the larger Turkish stones include: 157.66 (brown, emerald-cut—world's largest): 26.97 (light brown, oval); 10.63 (light brown). |
| Formula | AIO(OH) + Mn. |
| Crystallography | Orthorhombic; crystals are elongated plates, acicular needles; also massive, foliated. |
| Refractive Index | 1.702-1.750 |
| Birefringence | 0.048 |
| Luminescence | Dull pale yellow in SW (Chester, Massachusetts), Turkish stones fluoresce green in SW. |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, UV-Short |
| Absorption Spectrum | Not diagnostic; Turkish stones show broad bands at 4710, 4630, 4540, and a sharp line at 7010. |
| Pleochroism | Strong in manganiferous variety: violet-blue/pale green/rose to dark red. |
| Optics | a = 1.702; β = 1.722; γ = 1.750. Biaxial (+). 2V = 85°. |
| Optic Sign | Biaxial + |
| Luster | Vitreous; pearly on cleavage. |
| Specific Gravity | 3.3-3.5; Turkish material 3.39. |
| Transparency | Translucent to transparent. |
| Phenomena | Chatoyancy (rare); color change. |
DIASPORE Dimorph of Boehmite.
Optics: a = 1.702; β = 1.722; γ = 1.750.
Biaxial (+). 2V = 85°.
Occurrence: In metamorphosed limestones, chloritic schists, and altered igneous rocks. Also in bauxite deposits.
Mamaris, Yagatan, Mugla Province, Turkey: gemmy, pale brown crystals of very large size.
Chester, Massachusetts: with corundum in emery deposit; some fragments cuttable.
Chester County Pennsylvania: fine transparent crystals up to 2 inches long and ¼ inch thick, colorless to brown; some cuttable. Hungary: good crystals.
Postmasburg district, South Africa: manganiferous variety.
Cornwall, England; Greenland; Norway; Sweden; France; Switzerland; Germany; Greece; USSR; Japan; China
Comments: Diaspore is hard enough to make a durable jewelry stone, but the typical light brownish color is not easy to sell. Despite the large Turkish material, this is a very rare gemstone indeed.
Name: From the Greek diaspeirein, meaning to scatter, because it falls apart in the hot flame of a blowpipe.
Turkey’s gemstones include well-known species such as diaspore, chalcedony, and jade, as well as unusual specimens of lesser-known gems. Learn…
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