Stibiotantalite
Stibiotantalite is extremely rare as a faceted gem. Stibiotantalite crystals are fairly rare and usually almost opaque or very heavily included, so transparent gems are extremely rare. Stibiotantalite is strongly birefringent which may give gems with any clarity a sleepy look due to doubling of the back facets when seen through the table. Clean, facetable crystals are extremely rare. These locations may be the only sources of facetable crystals: Rio Grande do Norte, Brazil; Alto Ligonha District, Zambezia Province, Mozambique; and in the USA at San Diego County, California.
Distribution: From the Greenbushes tin placers, Wodgina district, Western Australia. Large crystals at the Muiâne and other mines, Alto Ligonha, Mozambique. From the Benson mine, Mtoko, Zimbabwe. In the USA, from Topsham, Sagadahoc County, Maine; in California, in San Diego County, fine crystals from the Himalaya mine, Mesa Grande district; at the Katerina, Stewart, and Vandenburg mines, Pala district; and in the Little Three mine, Ramona district; in the Brown Derby pegmatite, Gunnison County, Colorado. In the Varuträsk pegmatite, 15 km northwest of Skellefteå, Västerbotten, Sweden. From the Voronya massif, Kola Peninsula, Russia. Found near Stak Nala, Gilgit district, Pakistan.
| Chemical Formula: | Sb(Ta,Nb)O4 |
| Antimony Tantalum Oxide | |
| Molecular Weight: | 366.70 gm |
| Composition: | Tantalum | 49.35 % | Ta | 60.25 % | Ta2O5 |
| Antimony | 33.20 % | Sb | 41.93 % | SbO2 | |
| Oxygen | 17.45 % | O | |||
| 100.00 % | 102.18 % | = TOTAL OXIDE |
| Crystallography: | Orthorhombic – Pyramidal |
| Crystal Habit: | Crystals prismatic || [010], flattened || to [001], may be equant, to 12 cm; {001} and {101} striated || [010]. |
| Twinning: | About [010] with composition plane {001}; polysynthetic. |
| Cleavage: | Distinct on {001}, Indistinct on {100} |
| Fracture: | Sub-Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 5.5 |
| Density: | 5.98 – 7.53 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Color: | Yellow, greenish yellow, yellowish brown, reddish brown, brown |
| Transparency: | Transparent to Translucent |
| Luster: | Adamantine to Resinous |
| Refractive Index: | 2.374 – 2.457 Biaxial ( + ) |
| Birefringence: | 0.0826 |
| Dispersion: | 0.146; Relatively Strong; r < v |
| Pleochroism: | Colorless |
