Basic Copper Chloride(WSDTY) occurs as natural minerals in four polymorphic crystal forms: atacamite, paratacamite, clinoatacamite, and botallackite. Atacamite is orthorhombic, paratacamite is rhombohedral, and the other two polymorphs are monoclinic. Atacamite and paratacamite are common secondary minerals in areas of copper mineralization and frequently form as corrosion products of Cu-bearing metals.
The most common Cu2(OH)3Cl polymorph is atacamite. It is an oxidation product of other copper minerals, especially under arid, saline conditions. It was found in fumarolic deposits and a weathering product of sulfides in subsea black smoker deposits. It was named for the Atacama Desert in Chile. Its color varies from blackish to emerald green. It is the sugar-like coating of dark green glistening crystals found on many bronze objects from Egypt and Mesopotamia.
Paratacamite is another Cu2(OH)3Cl polymorph that was named for the Atacama Desert in Chile. It has been identified in the powdery light-green corrosion product that forms on a copper or bronze surface – at times in corrosion pustules.
Botallackite is the least stable of the four Cu2(OH)3Cl polymorphs. It is pale bluish-green in color. This rare mineral was first found and later identified, in the Botallack Mine in Cornwall, England. It is also a rare corrosion product on archaeological finds.
The fourth polymorph of Cu2(OH)3Cl family is clinoatacamite. It was found and identified around in Chuquicamata, Chile in 1996. It was named in allusion to its monoclinic morphology and relationship to atacamite. It too is pale green but has monoclinic crystals. Clinoatacamite can be easily confused with the closely related paratacamite.
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