Tantalite-(Fe)
Tantalite-(Fe) is a fairly rare mineral that is rarely available as a faceted gem. It is closely related to Tantalite-(Mn),Columbite-(Fe) and Tapiolite-(Fe). Tantalite and Columbite are often grouped together as a semi-singular mineral called Columbite-Tantalite or Coltan. However, Tantalite has a much greater specific gravity than Columbite (up to 8.0 for Tantalite compared to Columbite’s 5.2). Iron- rich Tantalite is the mineral Tantalite-(Fe), formerly known as Ferrotantalite, and manganese-rich Tantalite is Tantalite-(Mn), formerly known as Manganotantalite.
Tantalite is also very closely related to Tapiolite. The two minerals have the same chemical composition, but different crystal structures; Orthorhombic for Tantalite and Tetragonal for Tapiolite.Tantalite is found as brown to black opaque crystals and Manganotantalite can be found as brown to red translucent to transparent crystals and is rarely available as faceted gems that can be very attractive. Some Tantalite specimens may show a bluish iridescence and have weak magnetism.Material analyzed by microprobe from: Moss, Norway. At Spittal an der Drau, Austria. In the Yellowknife district, Northwest Territories, Canada. At Muhembe, Rwanda. From Nyanga, Uganda. At Upper Bear Gulch, Lawrence County, South Dakota, USA.
| Chemical Formula: | FeTa2O6 | ||||||||||||||||||||
| Iron Tantalum Oxide | |||||||||||||||||||||
| Molecular Weight: | 513.74 gm | ||||||||||||||||||||
| Composition: |
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| Crystallography: | Orthorhombic – Dipyramidal |
| Crystal Habit: | Commonly as exsolution intergrowths with ferrotapiolite. |
| Twinning: | None |
| Cleavage: | {100} Distinct, {010} less Distinct |
| Fracture: | Irregular/Uneven, Sub-Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 6.0 – 6.5 |
| Density: | 6.65 – 7.95 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Other: | Paramagnetic |
| Color: | Iron-Black; Reddish Brown in transmitted light; Gray in reflected light with Red to Reddish Brown internal reflections |
| Transparency: | Opaque, translucent on thin edges |
| Luster: | Vitreous, Submetallic |
| Refractive Index: | 2.260 – 2.430 Biaxial ( – ) |
| Birefringence: | 0.170 |
| Dispersion: | Relatively Strong; r < v |
