Erythrite

Erythrite
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]

For other uses, see Cobalt ochre.

Erythrite, also known as red cobalt, previously cobalt ochre[5]: 172  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 crystals

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]

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 köttigite (Zn).

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
2. Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (2005). "Erythrite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved 27 July 2022.
3. "Erythrite". Mindat.org. Retrieved 27 July 2022.
4. Barthelmy, David (2014). "Erythrite Mineral Data". Webmineral.com. Retrieved 27 July 2022.
5. Krivovichev V. G. Mineralogical glossary. Scientific editor A. G. Bulakh. — St.Petersburg: St.Petersburg Univ. Publ. House. 2009. — 556 p. — ISBN 978-5-288-04863-0

Further reading

• 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" (PDF). The Canadian Mineralogist. 9: 492–504.