MANGANOTANTALITE: Alta Ligonha, Mozambique (5.5). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Manganotantalite makes a spectacular red brown gem that is a very rare collector’s item. Transparent material is light enough in color to allow lots of light to enter and leave a cut gem, and properly cut stones are lively and brilliant. Cutting is difficult because of the cleavage.
| Data | Value |
|---|---|
| Name | Manganotantalite |
| Is a Variety of | Tantalite |
| Colors | Brownish black, reddish brown, scarlet red. |
| Crystallography | Orthorhombic. Crystals short prismatic; massive. |
| Refractive Index | 2.19-2.34 |
| Luster | Vitreous to resinous. |
| Hardness | 5.5-6.5. |
| Fracture | Subconchoidal to uneven |
| Specific Gravity | Mozambique material: 7.73-7.97. |
| Birefringence | 0.150 |
| Cleavage | Distinct 1 direction |
| Dispersion | High. |
| Stone Sizes | Cuttable crystals seldom reach 1 inch in size, and gems over 10 carats are rarities. However, the material is so dense that even a small stone is relatively heavy. Devonian Group (Calgary, Alberta, Canada): 3.05 (red-brown, Brazil). |
| Luminescence | None. |
| Luminescence Present | No |
| Transparency | Transparent to opaque. |
| Absorption Spectrum | Not diagnostic. |
| Formula |
(Mn,Fe)(Ta,Nb)2O6; Mn: Fe=3:1. |
| Pleochroism |
Shades of brown and red-brown. Also deep red/pale pink. |
| Optics |
α = 2.19; β = 2.25; γ = 2.34. Biaxial (+); 2V large. |
| Optic Sign | Biaxial + |
Series to Manganocolumbite;
Ferrotantalite; Columbotantalite.
Streak: Dark red.
Occurrence: In granite pegmatites; sometimes in placer deposits.
Pala, California; Portland, Connecticut; Amelia, Virginia.
Andilana, Madagascar; Sanarka River, Urals, USSR;
Sweden; Wodgina, Western Australia.
Minas Gerais, Brazil: facetable crystals.
Alta Ligonha, Mozambique: gem quality crystals. A150 from the Morrua Mine, Zambesia.
Comments: Manganotantalite makes a spectacular red brown gem that is a very rare collector’s item. Transparent material is light enough in color to allow lots of light to enter and leave a cut gem, and properly cut stones are lively and brilliant. Cutting is difficult because of the cleavage.
Name: After the composition, a manganiferous tantalite.
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