Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC-BY-SA-3.0], via Wikimedia Commons
The color of Namibian nambulite is a striking orange-red, very intense, and not really like any other gem I have seen. Cut stones would be both extremely rare and quite magnificent, perhaps bearing some similarities to rhodonite.
| Data | Value |
|---|---|
| Name | Nambulite |
| Colors | Reddish brown, orange-brown, orange. |
| Stone Sizes | Gems up to about 10 carats could potentially be cut from Namibian crystals. |
| Formula | NaLiMn8Si10O28(OH)2 |
| Hardness | 6.5 |
| Cleavage | Perfect 1 direction, distinct 1 direction |
| Crystallography | Triclinic. Crystals prismatic, flattened, and wedge shaped. |
| Refractive Index | 1.707-1.730 |
| Birefringence | 0.023 |
| Dispersion | Weak. |
| Luminescence | No data. |
| Luminescence Present | No |
| Absorption Spectrum | Not diagnostic. |
| Pleochroism | Weak. |
| Optics | a = 1.707; β = 1.710; γ = 1.730. Biaxial (+), 2V= 30°. |
| Optic Sign | Biaxial + |
| Luster | Vitreous. |
| Specific Gravity | 3.51 |
| Transparency | Transparent. |
Optics: a = 1.707; β=1.710; γ=1.730.
Biaxial (+), 2V= 30°.
Occurrence: Nambulite is a rare mineral reported in crystals up to 8 mm long at the Tunakozawa Mine, Northeast Japan. These crystals are found in veins cutting manganese oxide ores. Much larger crystals, up to approximately 3 cm across, have more recently been found in Namibia, at the Kombat Mine, near Tsumeb. I have seen a completely transparent crystal in a private collection that would yield about 20-25 carats of flawless faceted gems, the largest of these perhaps 10 carats in weight.
Comments: The color of Namibian nambulite is a striking orange-red, very intense, and not really like any other gem I have seen. Cut stones would be both extremely rare and quite magnificent, perhaps bearing some similarities to rhodonite.
Name: After Professor Matsuo Nambu of Tohoku University, Japan, for his studies of manganese minerals.
IGS Newsletter
