Crystal structure and chemistry of natural kutinaite from Černý Důl, Krkonoše, Czech Republic
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Crystal structure and chemistry of natural kutinaite from Černý Důl, Krkonoše, Czech Republic. / Bindi, Luca; Makovicky, Emil.
In: Mineralogical Magazine, Vol. 79, No. 5, 2015, p. 1099-1109.Research output: Contribution to journal › Journal article › Research › peer-review
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TY - JOUR
T1 - Crystal structure and chemistry of natural kutinaite from Černý Důl, Krkonoše, Czech Republic
AU - Bindi, Luca
AU - Makovicky, Emil
PY - 2015
Y1 - 2015
N2 - We have characterized the crystal structure of natural kutinaite, a rare mineral from the ores of Černý Důl, Czech Republic, by single-crystal X-ray diffraction and chemical analysis. We found that the structure of natural kutinaite is not identical to that of synthetic Cu14Ag6As7, previously reported to be cubic, space group Pm3m. Although topologically similar, the structure of natural kutinaite is indeed tetragonal, space group P4/mmm, with cell parameters: a = 11.789(2), c = 11.766(2) Å, V = 1635.5(4) Å3 and Z = 4. Electron microprobe analyses pointed to the (K,Tl)0.25Cu14Ag6As6.75 stoichiometry (Z = 4), or (K, Tl)Cu56Ag24As27 with Z = 16. The crystal structure of an untwinned crystal has been refined to R 1 = 2.61%. It consists of clusters of eight edge-sharing tetrahedra of Cu, which alternate in a 3D chess-board manner with octahedral clusters of six Ag atoms. The latter are surrounded by triangularly coordinated copper in eight faces of a cuboctahedron. The last structure components are large cavities containing partly occupied (K,Tl) sites, coordinated by 18 Ag and As ligands. The structure is full of direct metal-metal contacts although As plays the role of anion, associating especially with copper.
AB - We have characterized the crystal structure of natural kutinaite, a rare mineral from the ores of Černý Důl, Czech Republic, by single-crystal X-ray diffraction and chemical analysis. We found that the structure of natural kutinaite is not identical to that of synthetic Cu14Ag6As7, previously reported to be cubic, space group Pm3m. Although topologically similar, the structure of natural kutinaite is indeed tetragonal, space group P4/mmm, with cell parameters: a = 11.789(2), c = 11.766(2) Å, V = 1635.5(4) Å3 and Z = 4. Electron microprobe analyses pointed to the (K,Tl)0.25Cu14Ag6As6.75 stoichiometry (Z = 4), or (K, Tl)Cu56Ag24As27 with Z = 16. The crystal structure of an untwinned crystal has been refined to R 1 = 2.61%. It consists of clusters of eight edge-sharing tetrahedra of Cu, which alternate in a 3D chess-board manner with octahedral clusters of six Ag atoms. The latter are surrounded by triangularly coordinated copper in eight faces of a cuboctahedron. The last structure components are large cavities containing partly occupied (K,Tl) sites, coordinated by 18 Ag and As ligands. The structure is full of direct metal-metal contacts although As plays the role of anion, associating especially with copper.
U2 - 10.1180/minmag.2015.079.5.06
DO - 10.1180/minmag.2015.079.5.06
M3 - Journal article
VL - 79
SP - 1099
EP - 1109
JO - Mineralogical Magazine
JF - Mineralogical Magazine
SN - 0026-461X
IS - 5
ER -
ID: 160086141