- Erythrite
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Erythrite 
Erythrite crystalsGeneral Category Arsenate mineral Chemical formula Co3(AsO4)2·8H2O Strunz classification 08.CE.40 Dana classification 40.03.06.03 Vivianite group 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 Crystal system Monoclinic - Prismatic H-M Symbol (2/m) Space Group: 2/m 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; 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
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 kottigite (Zn).
References
- ^ a b c http://rruff.geo.arizona.edu/doclib/hom/erythrite.pdf Handbook of Mineralogy
- ^ a b http://www.mindat.org/min-1407.html Mindat.org
- ^ a b http://webmineral.com/data/Erythrite.shtml Webmineral data
- Dana's Manual of Mineralogy ISBN 0-471-03288-3
- Manual of Mineral Science, 22nd Ed. C. Klein.ISBN 0-471-25177-1
- Faye, G H; Nickel, E H (1968). "The origin of pleochroism in erythrite". The Canadian Mineralogist 9: 492–504. http://rruff.info/rruff_1.0/uploads/CM9_492.pdf.
Categories:- Cobalt minerals
- Arsenate minerals
- Monoclinic minerals
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