TURANITE, CU2+5 (V5+O42 (OH)4, FROM THE TYUYA-MUYUN RADIUM-URANIUM DEPOSIT, OSH DISTRICT, KYRGYZSTAN: A NEW STRUCTURE FOR AN OLD MINERAL

Abstract

The crystal structure of turanite, Cu 2+ 5 (V 5+ O 4) 2 (OH) 4 , from the Tyuya–Muyun Ra–U deposit, the Alai Ridge foothills, Osh district, Kyrgyzstan, triclinic, space group P ¯ 1, a 5.3834(2), b 6.2736(3), c 6.8454(3) Å, 86.169(1), 91.681(1), 92.425(1)°, V 230.38(2) Å 3 , Z = 1, has been solved by direct methods and refined to an R index of 2.2% based on 1332 observed [F o > 4F] unique reflections measured with MoK X-radiation and a Bruker P4 diffractometer equipped with a CCD detector. Chemical analysis by electron microprobe gave CuO 62.94, V 2 O 5 28.90, H 2 O 5.85, sum 97.69 wt.%; the amount of H 2 O was determined by crystal-structure analysis. The resulting empirical formula on the basis of 12 anions (including OH = 4 apfu) is Cu 2+ 4.97 (V 5+ O 4) 2 (OH) 4.08 . There are three distinct Cu sites fully occupied by Cu 2+ and octahedrally coordinated by four O atoms and two (OH) groups, with <Cu–O,OH> = 2.115 Å. The (Cu 6) octahedra (= O, OH) form a sheet of edge-sharing octahedra (with vacancies, oct : vac = 5 : 1) parallel to (011). On each side of the vacant octahedron, a (VO 4) tetrahedron is attached to three anions of the sheet and points away from the sheet to be attached to an anion of the adjacent sheet. Thus the (Cu 6) octahedra and (VO 4) tetrahedra constitute a framework, within which the sheets are also linked by hydrogen bonding from (OH) groups of one sheet to O anions of adjacent sheets. Turanite can be considered as a framework structure with interrupted sheets of (Cu 6) octahedra decorated by (VO 4) tetrahedra, and is related to the structures of cornubite, cianciulliite, gordaite, bechererite, chalcophyllite, ramsbeckite and simonkolleite.