Gaudefroyite
Gaudefroyite may be a comparatively rare salt mineral however very uncommon as a gem that’s faceted. Crystals sometimes area unit terribly skinny and tiny to concerning 10 millimetres long by 5 millimetres wide. it’s additionally a gem that’s uncommon it extremely is black and unnoticeable and solely out there as a collector’s oddity. Another gem that’s rare enthusiasts of Black Gems.
There are only two localities that are main for deposits of Gaudefroyite; at Tachgagalt, 17 km south-southwest of Ouarzazate, Anti-Atlas Mountains, Morocco. At the Ebony Rock, Wessels and N’Chwaning mines, Kalahari fields that are manganese near Kuruman, Cape Province, South Africa.
| Chemical Formula: | Ca4Mn3+3-X(BO3)3(CO3)(O,OH)3 |
| Calcium Manganese Borate Hydroxide | |
| Molecular Weight: | 582.85 gm |
| Composition: | Calcium | 27.51 % | Ca | 38.49 % | CaO |
| Manganese | 23.56 % | Mn | 33.86 % | Mn2O3 | |
| Boron | 5.56 % | B | 17.92 % | B2O3 | |
| Hydrogen | 0.13 % | H | 1.16 % | H2O | |
| Carbon | 2.06 % | C | 7.55 % | CO2 | |
| Oxygen | 41.18 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Hexagonal – Pyramidal |
| Crystal Habit: | Crystals are stubby dipyramidal {1120}, or prismatic {0110} with prominent pyramidal terminations, to 5 cm; typically as stepwise tapered crystals in divergent aggregates. |
| Twinning: | None |
| Cleavage: | None |
| Fracture: | Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 6.0; VHN = 840 |
| Density: | 3.35 – 3.50 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Color: | Black; in reflected light, Gray with strong Yellow-Orange to Reddish internal reflections. |
| Transparency: | Opaque, Transparent in thin slivers |
| Luster: | Vitreous to Dull, Adamantine to Resinous |
| Refractive Index: | w = 1.805 – 1.810 e = 2.015 – 2.020; Uniaxial ( + ) |
| Birefringence: | 0.210 |
| Dispersion: | n/a |
| Pleochroism: | Strong; O = pale yellowish brown; E = red-orange. w = 1.81(1) e = 2.02(1) |
| Anisotrophism: | Strong, in pale gray |
