Tantalite-(Mn)
Manganotantalite is a mineral with very high density so even small gems are relatively heavy. It also has high dispersion and makes for a beautiful gem when properly cut although gems are usually just translucent. Gems are very rare and difficult to cut because of the cleavage.
The main sources of gemmy to semi-gemmy crystals are Konar Province, Afghanistan; Alto do Giz pegmatite, Rio Grande do Norte, Northeast Region, Brazil; Murrua, Alto Ligonha District, Zambezia Province, Mozambique; and Mbarara District, Uganda.
| Category: | Columbite Group |
| Formula: | (Fe, Mn)Ta2O6 |
| Crystallography: | Orthorhombic – Dipyramidal |
| Crystal Habit: | Crystals short prismatic or equant, also tabular; in groups of parallel or subparallel crystals; massive (by analogy to Ferrocolumbite). |
| Twinning: | On [021] and [023], may produce pseudohexagonal trillings |
| Cleavage: | [100] Distinct, [010] less Distinct |
| Fracture: | Sub-Conchoidal to Irregular/Uneven |
| Tenacity: | Brittle |
| Hardness (Mohs): | 6.0 |
| Density: | 6.65 – 8.00 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Color: | Pink to nearly Colorless, Redish Brown to Black |
| Transparency: | Opaque to Translucent |
| Luster: | Vitreous, Sub-Metallic |
| Refractive Index: | 2.14 – 2.34 Biaxial ( + ) |
| Birefringence: | 0.080 – 0.200 |
| Dispersion: | Strong; r < v |
| Pleochroism: | Strong; X = red, Y = red brown, Z = orange |
