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The crystal structure of khinite and polytypism in khinite and parakhinite

¹ Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada, R3T 2N2
² Department of Earth Sciences, Royal Ontario Museum, 100 Queen’s Park, Toronto, Ontario, Canada, M5S 2C6

^* E-mail: frank_hawthorne{at}umanitoba.ca

The crystal structure of khinite, Pb²⁺Cu₃²⁺ Te⁶⁺O₆(OH)₂, orthorhombic, a = 5.7491(10), b = 10.0176(14), c = 24.022(3) Å, V = 1383.6(4) ų, space group Fdd2, Z = 8, D_calc = 6.29 g/cm³, from the Empire mine, Tombstone, Arizona, USA, has been solved by direct methods and refined to R₁ = 3.2% on the basis of 636 unique observed reflections. There is one distinct Te site occupied by Te and coordinated by six O atoms in an octahedral arrangement with a <Te–O> distance of 1.962 Å, typical of Te⁶⁺. There are three octahedrally-coordinated Cu sites, each of which is occupied by Cu²⁺ with <Cu–O> distances of 2.132, 2.151 and 2.308 Å, respectively. Each Cu octahedron shows four short meridional bonds (~1.95 Å) and two long apical bonds (2.46–2.99 Å) characteristic of Jahn-Teller-distorted Cu²⁺ octahedra. There is one distinct Pb site occupied by Pb and coordinated by six O atoms and two (OH) groups with a <Pb–O, OH> distance of 2.690 Å. Te₆ and Cu₆ octahedra share edges and corners to form an [M₂] (where = O, OH) layer of composition [TeCu₃₈]. These layers stack along the c axis at 6 Å intervals with Pb atoms between the layers. Identical layers occur in the structure of parakhinite, Pb²⁺Cu₃²⁺ Te⁶⁺O₆(OH)₂, hexagonal, a = 5.765(2), c = 18.001(9) Å, V = 518.0(4) Å ³, space group P3₂, Z = 3, D_calc = 6.30 g/cm³. It is only the relative stacking of the TeCu₃8 layers in the c direction that distinguishes the two structures, and hence khinite and parakhinite are polytypes.

KEYWORDS: khinite, tellurate, Cu mineral, parakhinite, polytypism

This article has been cited by other articles:

				F. C. Hawthorne, M. A. Cooper, and M. E. Back KHINITE-4O [= KHINITE] AND KHINITE-3T [= PARAKHINITE] Can Mineral, April 1, 2009; 47(2): 473 - 476. [Abstract] [Full Text] [PDF]