Rosasite
Rosasite forms in the oxidation zones of zinc-copper deposits and typically found as crusts and botryoidal masses or nodules. Crystals are an attractive bluish-green and fibrous. Because of this, gems are rare and are usually opaque or translucent at best but still very attractive because of the bright color and pearly, fibrous structure.
Rosasite is found in a number of localities worldwide including the type locality of Rosas mine, Sulcis, Sardinia, Italy. At a number of places in England, such as Caldbeck Fells, Cumbria, and mines in Cornwall. Fine examples from Tsumeb, Namibia. In the USA, from the Kelly mine, Magdalena, Socorro County, New Mexico; fine specimens from the Silver Bill mine, Gleeson, and at Bisbee, Cochise County, in the 79 mine, Gila County, and a number of other places in Arizona; from the Mohawk mine, San Bernardino County, California; at Leadville, Lake County, Colorado; from Majuba Hill, Pershing County, Nevada; in the Hidden Treasure mine, Ophir district, Tooele County, Utah. Abundant specimens from the Ojuela mine, Mapimí, Durango, Mexico. In small amounts from additional localities.
| Category: | Carbonate mineral |
| Chemical Formula: | Cu,Zn2(CO3)(OH)2 |
| Copper Zinc Carbonate Hydroxide | |
| Molecular Weight: | 222.04 gm |
| Composition: | Zinc | 14.72 % | Zn | 18.33 % | ZnO |
| Copper | 42.93 % | Cu | 53.74 % | CuO | |
| Hydrogen | 0.91 % | H | 8.11 % | H2O | |
| Carbon | 5.41 % | C | 19.82 % | CO2 | |
| Oxygen | 36.03 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | Crystals are acicular, to 0.5 mm; in radial or divergent sprays or globular; compact mammillary to botryoidal crusts and masses, typically fibrous and with warty surfaces. |
| Twinning: | On {100} |
| Cleavage: | Distinct/Good in two directions at right angles. |
| Fracture: | Splintery – Thin, elongated fractures produced by intersecting good cleavages or partings. |
| Tenacity: | Brittle |
| Moh’s Hardness: | 4.5 |
| Density: | 4.00 – 4.20 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Other: | Soluble in acids |
| Color: | Blue, Blue-Green to Green, sky-Blue; Colorless to light blue in transmitted light. |
| Transparency: | Translucent |
| Luster: | Vitreous, Silky |
| Refractive Index: | 1.672 – 1.831 Biaxial ( – ) |
| Birefringence: | 0.139 – 0.140 |
| Dispersion: | Strong; r > v |
| Pleochroism: | Strong; X = pale emerald-green; Z = dark emerald-green |
