Melanite
Melanite is a black, titanium-rich, variety of Andradite Garnet. The Andradite variety of the Garnet Group of minerals includes Melanite (black), Demantoid (green) and Topazolite (yellow). Melanite’s black color is due to its high titanium content and is occassionally referred to as “titanian adradite”.
Although there are many localities for Melanite, there are three that are known for crystals large enough for faceting: Nioro du Sahel Circle, Kayes Region, Mali; Chihuahua, Mexico; Dallas Gem Mine (Benitoite Mine), Diablo Range, San Benito County, California, USA.
| Chemical Formula: | Ca3Fe3+2(SiO4)3 + Ti |
| Calcium Iron Titanium Silicate | |
| Molecular Weight: | 508.18 gm (Andradite) |
| Composition: | Calcium | 23.66 % | Ca | 33.11 % | CaO |
| (based on Andradite): | Iron | 21.98 % | Fe | 28.28 % | FeO |
| Silicon | 16.58 % | Si | 35.47 % | SiO2 | |
| Titanium | ?? % | Ti | ?? % | TiO2 | |
| Oxygen | 37.78 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Isometric – Hexoctahedral |
| Crystal Habit: | Commonly well-crystallized dodecahedra, trapezohedra, or combinations, to 5 cm. Also granular to massive. |
| Twinning: | None |
| Cleavage: | None |
| Fracture: | Irregular/Uneven, Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 6.5 – 7.0 |
| Density: | 3.80 – 3.90 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Color: | Black |
| Transparency: | Opaque |
| Luster: | Adamantine, Resinous, Dull |
| Refractive Index: | 1.887 Isotropic |
| Birefringence: | 0.000 (Isotropic) |
| Dispersion: | Andradite: 0.057 |
| Pleochroism: | None |
| Anisotrophism: | Typically Weak |
