Manganite
Manganite was at one time a valuable manganese ore. It has been so heavily mined that it is now somewhat of a rarity and is considered a minor ore despite its high manganese content. Fine crystals were once found at Ilfeld, Harz Mountains and Ilmenau, Thuringia, Germany. Manganite is opaque black with sub-metallic luster and can be added to the list of black gems for collectors.
Manganite is found at many localities worldwide, but rarely well-crystallized. Fine crystals from Ilfeld, Harz Mountains, and Ilmenau, Thuringia, Germany. In the Botallack mine, St. Just, Cornwall; from Egremont, Cumbria; and at Upton Pyne, Exeter, Devonshire, England. From Granam, near Towie, Aberdeenshire, Scotland. At Bölet, near Karlsborg, Västergötland,Sweden. In the USA, good crystals from the Negaunee and Marquette districts, Marquette County, Michigan; in the Powell’s Fort mine, near Woodstock, Shenandoah County, Virginia; and at Lake Valley, Sierra County, New Mexico. From the Caland mine, Atikokan, Ontario, Canada. At Kuruman, Cape Province, South Africa.
| Category: | Oxide mineral |
| Chemical Formula: | Mn3+O(OH) |
| Manganese Oxide Hydroxide | |
| Molecular Weight: | 87.94 gm |
| Composition: | Manganese | 62.47 % | Mn | 89.76 % | Mn2O3 |
| Hydrogen | 1.15 % | H | 10.24 % | H2O | |
| Oxygen | 36.39 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | Crystals prismatic and striated || [001], short to long, to 7.5 cm; typically terminated by {001}, {h0l}, may be complex. In bundles, subparallel [001], fibrous; granular, massive. |
| Twinning: | Contact and penetration twins on {011}; lamellar on {100}. |
| Cleavage: | {010} Perfect, {110} and {001} Good |
| Fracture: | Irregular/Uneven |
| Tenacity: | Brittle |
| Moh’s Hardness: | 4.0 |
| Density: | 4.29 – 4.34 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Color: | Dark steel-Gray to iron-Black; Red-Brown in transmitted light; in reflected light, Gray-White with Brownish tint, with blood-red internal reflections |
| Transparency: | Opaque, transparent on thin edges |
| Luster: | Sub-metallic |
| Refractive Index: | 2.250 – 2.530 Biaxial ( + ) |
| Birefringence: | 0.280 |
| Dispersion: | Extreme; r > v |
| Pleochroism: | Weak, Faint; X = reddish brown; Z = red-brown |
| Anisotrophism: | Weak; Color in reflected light: gray-white with brown tint; Internal reflections: blood red; Bireflectance: distinct in grays |
