Plancheite
Plancheite was named after a French explorer, J. Planche, who supplied samples to Alfred Lacroix from Mindouli who first described the mineral in 1908. The samples were found by Planche at the Sanda Mine, Mindouli, Pool Department, Republic of Congo. The chemical formula of Plancheite is Cu8Si8O22(OH)4 • 2H2O (Hydrated Copper Silicate Hydroxide) and its molecular weight is 1,171.08 gm. Plancheite is a rare secondary mineral formed in the oxidation zone of copper deposits. Plancheite has a specific gravity of 3.65 – 3.80 (g/cm3) and the refractive index of 1.645 – 1.715 Biaxial ( + ). It is a hydrated copper silicate mineral and is closely related to Shattuckite in structure and appearance. The two minerals are often confused. Like so many other secondary copper minerals, Plancheite is colorful, attractive and has interesting crystal habits that are typically fibrous, compact radial aggregates. It is often found associated with other colorful secondary copper minerals such as Chrysocolla, Conichalcite, Dioptase, Malachite, Shattuckite and Brochantite.
Distribution: From Mindouli, Renéville, and Tshiniama, Congo Republic. In Congo (Zaire), fine material from Tantara, Mindi, and M’sesa, near Kambove, Katanga (Shaba) Province. From Tsumeb, Guchab, and Okatumba, about 80 km east of Windhoek, Namibia. In England, at the Driggith mine, Caldbeck Fells, Cumbria; the Gunheath china clay pit, St. Austell, Cornwall; and the Engine Vein, Alderley Edge, Cheshire. In the USA, in Arizona, from the Table Mountain mine, Galiuro Mountains, and the Azurite mine, Tortolita Mountains, Pinal County; in the Bighorn district, south of Aguila, Maricopa County; in the Harquehala Mountains, Yuma County; and elsewhere. In Michigan, from the Algomah mine, Ontonagon County. In the Kurokawa mine, Gifu Prefecture, and the Kisanmori mine, Akita Prefecture, Japan. From La Rioja, Argentina.
| Category: | Inosilicate |
| Chemical Formula: | Cu8Si8O22(OH)4 • 2H2O |
| Hydrated Copper Silicate Hydroxide | |
| Molecular Weight: | 1,171.08 gm |
| Composition: | Copper | 43.41 % | Cu | 54.34 % | CuO |
| Silicon | 19.19 % | Si | 41.05 % | SiO2 | |
| Hydrogen | 0.52 % | H | 4.62 % | H2O | |
| Oxygen | 36.89 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Orthorhombic – Dipyramidal |
| Crystal Habit: | Crystals fibrous by extension on [001], striated; commonly as compact radial aggregates. |
| Twinning: | None |
| Cleavage: | None |
| Fracture: | Unknown; crystals are too small to observe fractures |
| Tenacity: | Brittle, fibrous |
| Moh’s Hardness: | 6.0 |
| Density: | 3.65 – 3.80 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Color: | Pale blue to deep blue, pale greenish blue |
| Transparency: | Translucent |
| Luster: | Silky |
| Refractive Index: | 1.645 – 1.715 Biaxial ( + ) |
| Birefringence: | 0.070 |
| Dispersion: | Relatively strong |
| Pleochroism: | Visible, marked; X= pale blue, Y=Z= blue |
