Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC-BY-SA-3.0], via Wikimedia Commons
Cut stibiotantalite strongly resembles sphalerite, but the luster is much less brilliant (sphalerite can be adamantine), and stibiotantalite is usually more heavily included, as well as strongly birefringent. This birefringence gives the cut gems a sleepy look due to doubling of back facets as seen through the table. Cut gems over 2-3 carats are among the rarest of collector items.
Stibiotantalite Value
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Stibiotantalite Information
| Data | Value |
| Name | Stibiotantalite |
| Crystallography | Orthorhombic. Crystals prismatic, striated, often twinned, massive. |
| Colors | Dark brown to light yellowish brown, reddish yellow, yellowish gray, reddish brown, greenish, yellow. Often zoned. |
| Luster | Vitreous to resinous. |
| Hardness | 5-5.5. |
| Density | 7.34-7.46. |
| Birefringence | 0.090 |
| Cleavage | Distinct 1 direction. Fracture subconchoidal. Brittle. |
| Dispersion | 0.146. |
| Stone Sizes | This material is virtually unknown in cut stones over 10 carats. The material is fairly rare, but transparent specimens are extremely rare. Devonian Group (Calgary, Alberta, Canada): 4.65 (Brazil). Smithsonian Institution (Washington, D.C): 7.3 (yellow. Brazil); 2.5 (brown, Mozambique). |
| Luminescence | None. |
| Spectral | Not diagnostic; may show “didymium” lines. |
| Formula | Sb(Ta,Nb)O4. |
Series to Tantalite.
Streak: Yellow-brown.
Optics: a = 2.37; β= 2.40; γ=2.46.
Biaxial (+), 2V=75°.
Occurrence: In granite pegmatites, often in good crystals.
Topsham, Maine, San Diego County, California: gemmy crystals.
Varuträsk, Sweden. Wodgina district Western Australia: as rolled pebbles.
Brazil; Mozambique: gemmy crystals.
Comments: Cut stibiotantalite strongly resembles sphalerite, but the luster is much less brilliant (sphalerite can be adamantine), and stibiotantalite is usually more heavily included, as well as strongly birefringent. This birefringence gives the cut gems a sleepy look due to doubling of back facets as seen through the table. Cut gems over 2-3 carats are among the rarest of collector items.
Name: In allusion to the composition.
