Botallackite

Botallackite, chemical formula Cu2(OH)3Cl is a secondary copper mineral, named for its type locality at the Botallack Mine, St Just in Penwith, Cornwall. It is polymorphous with atacamite, paratacamite and clinoatacamite.[1]

Botallackite
Botallackite from the Levant Mine, Cornwall
General
CategoryHalide minerals
Formula
(repeating unit)
Cu2(OH)3Cl
Strunz classification3.DA.10b
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/m
Unit cella = 5.717 Å,
b = 6.126 Å,
c = 5.636 Å; β = 93.07°; Z = 2
Identification
ColourShades of green
Crystal habitPlaty interlaced crystal crusts
Cleavage{100} Perfect
Mohs scale hardnessSoft
DiaphaneityTransparent to translucent
Specific gravity3.6
Optical propertiesBiaxial (+)
Refractive indexnα= 1.775, nβ= 1.800, nγ= 1.846
Birefringenceδ = 0.071
PleochroismWeak - blue green shades
Dispersionr > v, strong
References[1][2][3]

Botallackite crystallises in the monoclinic crystal system. It is mountain-green to green in colour, with one distinct to good cleavage.[1]

Discovery and occurrence

It was first described in 1865 for an occurrence in the Botallack mine, Cornwall, England, and named for the type locality.[1]

Botallackite forms in copper deposits exposed to weathering and salt water.[1] It is reported from black smoker deposits due to reaction of primary sulfide minerals with seawater. It also occurs on copper bearing slag exposed to seawater. Minerals associated with botallackite include atacamite, paratacamite, brochantite, connellite and gypsum.[2]

References

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