| Erythrite | |
| Category: | Arsenate mineral |
| Boxbgcolor: |
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| Boxtextcolor: | white |
| Formula: | Co3(AsO4)2·8H2O |
| Imasymbol: | Ery[1] |
| Strunz: | 8.CE.40 |
| Dana: | 40.03.06.03 |
| System: | Monoclinic |
| Class: | Prismatic (2/m) (same H-M symbol) |
| Symmetry: | C2/m |
| Color: | Crimson to peach-red, pale rose, or pink, may be zoned |
| Habit: | Radial or stellate aggregates, fibrous, drusy; usually powdery and massive – rarely as striated prismatic crystals |
| Cleavage: | Perfect on ; poor on and . |
| Tenacity: | Sectile |
| Mohs: | 1.5–2.5 |
| Luster: | Subadamantine, pearly on cleavages |
| Streak: | Pale red to pink |
| Diaphaneity: | Transparent to translucent |
| Gravity: | 3.06 |
| Opticalprop: | Biaxial (+) |
| Refractive: | 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] |
Erythrite, also known as red cobalt, is a secondary hydrated cobalt arsenate mineral with the formula . Erythrite and annabergite, chemical formula, or nickel arsenate form a complete series with the general formula .
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,[3] and takes its name from the Greek έρυθρος (erythros), meaning red. 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.
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]
The nickel variety, annabergite, occurs as a light green nickel bloom on nickel arsenides. In addition iron, magnesium and zinc can also substitute for the cobalt position, creating three other minerals: parasymplesite (Fe), hörnesite (Mg) and köttigite (Zn).