Botallackite

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Botallackite
Botallackite-sea82b.jpg
Botallackite from the Levant Mine, Cornwall
General
Category Halide minerals
Formula
(repeating unit)
Cu2(OH)3Cl
Strunz classification 3.DA.10b
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P21/m
Unit cell a = 5.717 Å,
b = 6.126 Å,
c = 5.636 Å; β = 93.07°; Z = 2
Identification
Colour Shades of green
Crystal habit Platy interlaced crystal crusts
Cleavage {100} Perfect
Mohs scale hardness Soft
Diaphaneity Transparent to translucent
Specific gravity 3.6
Optical properties Biaxial (+)
Refractive index nα= 1.775, nβ= 1.800, nγ= 1.846
Birefringence δ = 0.071
Pleochroism Weak - blue green shades
Dispersion r > v, strong
References [1][2][3]

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

Discovery and occurrence[edit]

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[edit]