From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
Erythrite crystals
Category Arsenate mineral
Vivianite group
(repeating unit)
Strunz classification 8.CE.40
Dana classification
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group C2/m
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 [1][2][3]

Erythrite or red cobalt is a secondary hydrated cobalt arsenate mineral with the formula (Co3(AsO4)2·8H2O). Erythrite and annabergite (Ni3(AsO4)2·8H2O) (nickel arsenate) form a complete series with the general formula (Co,Ni)3(AsO4)2·8H2O.

Erythrite from Morocco

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.[2] 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.[1]

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.[1]

Other varieties[edit]

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).