| Erythrite | |
|---|---|
 Erythrite crystals | |
| General | |
| Category | Arsenate mineral |
| Formula (repeating unit) | Co3(AsO4)2·8H2O |
| IMA symbol | Ery[1] |
| Strunz classification | 8.CE.40 |
| Dana classification | 40.03.06.03 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | C2/m |
| Identification | |
| Color | Crimson to peach-red, pale rose, or pink, may be zoned |
| Crystal habit | Radial or stellate aggregates, fibrous, drusy; usually powdery and massive – rarely as striated prismatic crystals |
| Cleavage | Perfect on {010}; poor on {100} and {102}. |
| Tenacity | Sectile |
| Mohs scale hardness | 1.5–2.5 |
| Luster | Subadamantine, pearly on cleavages |
| Streak | Pale red to pink |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 3.06 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.626 – 1.629 nβ = 1.662 – 1.663 nγ = 1.699 – 1.701 |
| Birefringence | δ = 0.073 |
| Pleochroism | Visible: X = pale pinkish to pale rose; Y = pale violet to pale violet-rose; Z = deep red |
| References | [2][3][4] |
Erythrite or red cobalt is a secondary hydrated cobalt arsenate mineral with the formula Co
3(AsO
4)
2•8H
2O. Erythrite and annabergite, chemical formula Ni
3(AsO
4)
2•8H
2O, or nickel arsenate form a complete series with the general formula (Co,Ni)
3(AsO
4)
2•8H
2O.
Erythrite crystallizes in the monoclinic system and forms prismatic crystals. The color is crimson to pink and occurs as a secondary coating known as cobalt bloom on cobalt arsenide minerals. Well-formed crystals are rare, with most of the mineral manifesting in crusts or small reniform aggregates.
Erythrite was first described in 1832 for an occurrence in Grube Daniel, Schneeberg, Saxony,[4] and takes its name from the Greek έρυθρος (erythros), meaning red.[3] Historically, erythrite itself has not been an economically important mineral, but the prospector may use it as a guide to associated cobalt and native silver.[citation needed]
Erythrite occurs as a secondary mineral in the oxide zone of Co–Ni–As bearing mineral deposits. It occurs in association with cobaltite, skutterudite, symplesite, roselite-beta, scorodite, pharmacosiderite, adamite, morenosite, retgersite, and malachite.[2]
Notable localities are Cobalt, Ontario; La Cobaltera, Chile, Schneeberg, Saxony, Germany; Joachimsthal, Czech Republic; Cornwall, England; Bou Azzer, Morocco; the Blackbird mine, Lemhi County, Idaho; Sara Alicia mine, near Alamos, Sonora, Mexico; Mt. Cobalt, Queensland and the Dome Rock copper mine, Mingary, South Australia.[2]
