Original paper

Anatacamite from La Vendida mine, Sierra Gorda, Atacama desert, Chile: a triclinic polymorph of Cu2(OH)3Cl

Malcherek, Thomas; Schlüter, Jochen

Abstract

The new mineral anatacamite (IMA-CNMNC No. 2008-042) has the ideal chemical formula Cu2(OH)3Cl. It is triclinic with space group P1 Unit-cell data from single-crystal X-ray studies gave a = 9.1646(9), b = 9.2029(8), c = 9.2102(8) Å, α = 95.858(6)°, β = 96.290(7)°, γ = 96.507(2)°, V = 761.97(12) Å3, Z = 8. Anatacamite is the triclinic polymorph of atacamite, botallackite and clinoatacamite. The strongest reflections in the X-ray powder diffraction data, calculated from single crystal data, are as follows dobs. (Å) (I): 5.432 (100), 2.747 (94), 2.257 (56), and 2.889 (31). Anatacamite was found in La Vendida mine, Sierra Gorda mining district, northeast of Antofagasta, Chile. It occurs as triangular, tabular crystals up to 2 mm in size grown on prismatic atacamite crystals. Anatacamite shows emerald green colour with a vitreous luster. The crystals show a good cleavage parallel to {111}. The calculated density is 3.725 g/cm3, the calculated mean refractive index is 1.80, pleochroism is not apparent. In La Vendida mine anatacamite is closely associated with atacamite, further minerals of this mineralization are alunite, clinoatacamite, chalcanthite, coquimbite, eriochalcite, jarosite, kröhnkite, magnesioaubertite, tamarugite and voltaite. Chemical analyses gave (wt.%) CuO 74.24, ZnO 0.02, NiO 0.99, Cl 16.98, H2Ocalc 12.74, O ≡ Cl -3.84, sum 101.13. The resulting empirical formula basedon 4 anions pfu is Cu1.97Ni0.03(OH)2.99Cl1.01. Anatacamite is named for its triclinic symmetry and its polymorphism with atacamite. Type material is deposited in the collection of the Mineralogical Museum Hamburg, Germany.

Keywords

anatacamitebotallackiteclinoatacamiteatacamitecu2(oh)3clchileatacamasierra gordala vendida minerio tinto minecopper chloride hydroxide