Chalcophyllite
| Chalcophyllite | |
|---|---|
Chalcophyllite from the Ting Tang Mine, Carharrack, Cornwall, England. Photo by Rob Lavinsky | |
| General | |
| Category | Arsenate minerals |
| Formula | Cu 18Al 2(AsO 4) 4(SO 4) 3(OH) 24·36(H 2O) or Cu 18Al 2(AsO 4) 3(SO 4) 3(OH) 27·33(H 2O) |
| IMA symbol | Chp |
| Strunz classification | 8.DF.30 |
| Dana classification | 43.5.14.1 |
| Crystal system | Trigonal |
| Crystal class | Rhomboedral (3) H-M symbol: (3) |
| Space group | R3 |
| Identification | |
| Color | Blue-green to emerald-green |
| Crystal habit | Crystals platy and six-sided, also as rosettes, drusy, foliated or massive. |
| Twinning | On {1010} as twin plane. |
| Cleavage | Perfect on {0001} |
| Fracture | Irregular |
| Mohs scale hardness | 2 |
| Luster | Vitreous to subadamantine, pearly on {0001} |
| Streak | Pale green |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.67 to 2.69 or 2.4 to 2.66 |
| Optical properties | Uniaxial (−) |
| Refractive index | nω = 1.618 to 1.632, nε = 1.552 to 1.575 |
| Pleochroism | O blue-green, E almost colorless |
| Solubility | Soluble in acids and in ammonia |
| Other characteristics | Can be partially dehydrated. Alters to chrysocolla. Nonfluorescent, not radioactive |
| References | |
Chalcophyllite is a rare secondary copper arsenate mineral occurring in the oxidized zones of some arsenic-bearing copper deposits. It was first described from material collected in Germany. At one time chalcophyllite from Wheal Tamar in Cornwall, England, was called tamarite, but this name is now discredited (not to be confused with the amphibole mineral taramite, which is quite different). At Wheal Gorland a specimen exhibiting partial replacement of liriconite, Cu
2Al(AsO
4)(OH)
4·(4H
2O), by chalcophyllite has been found. The mineral is named from the Greek, chalco "copper" and fyllon, "leaf", in allusion to its composition and platy structure. It is a classic Cornish mineral that can be confused with tabular spangolite.