In:
Mineralogical Magazine, Mineralogical Society, Vol. 83, No. 4 ( 2019-08), p. 539-549
Kurzfassung:
The crystal structure of tlapallite has been determined using single-crystal X-ray diffraction and supported by electron probe micro-analysis, powder diffraction and Raman spectroscopy. Tlapallite is trigonal, space group P 321, with a = 9.1219(17) Å, c = 11.9320(9) Å and V = 859.8(3) Å 3 , and was refined to R 1 = 0.0296 for 786 reflections with I 〉 2σ( I ). This study resulted from the discovery of well-crystallised tlapallite at the Wildcat prospect, Utah, USA. The chemical formula of tlapallite has been revised to (Ca,Pb) 3 CaCu 6 [Te 4+ 3 Te 6+ O 12 ] 2 (Te 4+ O 3 ) 2 (SO 4 ) 2 ·3H 2 O, or more simply (Ca,Pb) 3 CaCu 6 Te 4+ 8 Te 6+ 2 O 30 (SO 4 ) 2 ·3H 2 O, from H 6 (Ca,Pb) 2 (Cu,Zn) 3 (TeO 3 ) 4 (TeO 6 )(SO 4 ). The tlapallite structure consists of layers containing distorted Cu 2+ O 6 octahedra, Te 6+ O 6 octahedra and Te 4+ O 4 disphenoids (which together form the new mixed-valence phyllotellurate anion [Te 4+ 3 Te 6+ O 12 ] 12− ), Te 4+ O 3 trigonal pyramids and CaO 8 polyhedra. SO 4 tetrahedra, Ca(H 2 O) 3 O 6 polyhedra and H 2 O groups fill the space between the layers. Tlapallite is only the second naturally occurring compound containing tellurium in both the 4 + and 6 + oxidation states with a known crystal structure, the other being carlfriesite, CaTe 4+ 2 Te 6+ O 8 . Carlfriesite is the predominant secondary tellurium mineral at the Wildcat prospect. We also present an updated structure for carlfriesite, which has been refined to R 1 = 0.0230 for 874 reflections with I 〉 2σ( I ). This updated structural refinement improves upon the one reported previously by refining all atoms anisotropically and presenting models of bond valence and Te 4+ secondary bonding.
Materialart:
Online-Ressource
ISSN:
0026-461X
,
1471-8022
Sprache:
Englisch
Verlag:
Mineralogical Society
Publikationsdatum:
2019
ZDB Id:
2034522-7
SSG:
13
