botallackite

{{Infobox mineral | name = Botallackite | category = Halide minerals | boxwidth = | boxbgcolor = | image = Botallackite-sea82b.jpg | imagesize = | caption = Botallackite from the Levant Mine, Cornwall | formula = Cu2(OH)3Cl | IMAsymbol=Blk | strunz = 3.DA.10b | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = P21/m | unit cell = a = 5.717 Å, b = 6.126 Å, c = 5.636 Å; β = 93.07°; Z = 2 | colour = Shades of green | habit = Platy interlaced crystal crusts | twinning = | cleavage = {100} Perfect | fracture = | tenacity = | mohs = Soft | luster = | polish = | refractive = nα= 1.775, nβ= 1.800, nγ= 1.846 | opticalprop = Biaxial (+) | birefringence = δ = 0.071 | dispersion = r > v, strong | pleochroism = Weak – blue green shades | fluorescence= | absorption = | streak = | gravity = 3.6 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent to translucent | other = | references = }} Botallackite, chemical formula Cu2(OH)3Cl is a secondary copper mineral, named for its type locality at the Botallack Mine in St Just in Penwith, Cornwall. It is polymorphous with atacamite, paratacamite and .

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