THE CRYSTAL STRUCTURE OF CLINOATACAMITE, A NEW POLYMORPH OF Cu2(OH)3Cl

JOEL D. GRICE
Research Division, Canadian Museum of Nature, P.O. Box 3443, Station "D", Ottawa, Ontario K1P 6P4

JAN T. SZYMANSKI
CANMET, Natural Resources Canada, 555 Booth Street, Ottawa, Ontario K1A 0G1

JOHN L. JAMBOR
Department of Earth Sciences, University of Waterloo, Waterloo, Ontario N2L 3G1

Abstract

The crystal structure of clinoatacamite, Cu22+(OH)3Cl, has been determined and refined to indices R = 5.2 and wR = 4.9%. The structure is monoclinic, space group P21/n (14), with cell parameters a 6.144(1), b 6.805(1), c 9.112(1) Å, 99.55(3) , V 375.7(2) Å3, and with Z = 4. The structure analysis was essential in determining the valence state of copper (Cu2+) and the number of (OH)- anions in the formula. The structure consists of layers of partly occupied, edge-sharing octahedra of Jahn-Teller-distorted [Cu(OH)4Cl2] octahedra parallel to (101). This layer is topologically the same as that in mica. Adjacent layers of octahedra are offset, such that vacant sites in one sheet align with occupied sites in the neighboring sheet. Layers are linked by individual, slightly Jahn- Teller-distorted octahedra of composition [Cu(OH)6]. The structures of paratacamite and the other polymorphs of Cu2(OH)3Cl, atacamite and botallakite, also are layered, but they differ from the layering of clinoatacamite in topology, composition and cross-linkage.