FRANKHAWTHORNEITE, A UNIQUE HCP FRAMEWORK STRUCTURE OF A CUPRIC TELLURATE*

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

ANDREW C. ROBERTS
Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8

* Geological Survey of Canada contribution number 30294.

Abstract

The crystal structure of frankhawthorneite, Cu22+Te6+ O4(OH)2, has been determined and refined to indices R = 5.4 and Rw = 4.6%. The structure is monoclinic P21/n (14), with cell parameters a 9.107(4), b 5.213(1), c 4.605(2) Å, 98.74(3) , V 216.1(1) Å3, and with Z = 2. The structure analysis was essential in determining the valence state of Cu2+ and Te6+ and the number of O2- and (OH)- anions in the formula. The crystal structure consists of a framework of edge-sharing octahedra. In the hexagonal closest packed (HCP) array of anions, one-half of the octahedrally coordinated sites are filled. The unique topology of the filled cation sites gives rise to a ribbon of alternating single [TeO4(OH)2]2- and double [CuO4(OH)2]8- octahedra.

Keywords: frankhawthorneite, crystal structure, tellurate, cupric, hexagonal closest packing.