Crystal structure of lindackerite, (Cu,Co,Ni)Cu4(AsO4)2(AsO3OH)2 9 H2O from Jachymov, Czech Republic
Hybler, Jiří Ondruš; Císařová, Ivana; Petříčec, Václav; Veselovský, František
European Journal of Mineralogy Volume 15 Number 6 (2004), p. 1035 - 1042
published: Jan 5, 2004
ArtNo. ESP147051506011, Price: 29.00 €
Two crystals of lindackerite, ideally (Cu,Co,Ni)Cu4(AsO4)2 (AsO3OH)2 Â· 9 H2O from JÃ¡chymov (formerly St. Joachimsthal), Czech Republic, were studied and found to be essentially isostructural. The microprobe analysis of the first sample yielded (in wt%): As 29.66, Cu 27.85, Co 1.50, Ni 0.83, O 39.96, sum 99.79, (Cu0.43Co0.26Ni0.14)∑0.83 Cu4.00[(AsO4)1.66(AsO3OH)2.34] Â· 9.24 H2O, P1, a = 6.440(2), b = 8.065(3), c = 10.411(5) Ã , Î± = 85.44(4)Â°, Î² = 79.38(3)Â°, Î³ = 84.65(3)Â°, V = 528.1(3) Ã 3, Z = 1, Dcalc = 3.261 g/cm3. The structure was refined to Robs = 5.03 %. The second crystal was an end member, without any Co, Ni yielded (in wt%): As 30.66, Cu 31.76, Co < 0.01, ni < 0.01, o 39.30, sum 101.75, cu0.89Cu4.00[(AsO4)1.78(AsO3OH)2.22] Â· 8.01 H2O, a = 6.415(1), b = 8.048(1), c = 10.332(1) Ã , Î± = 85.41(1)Â°, Î² = 79.50(1)Â°, Î³ = 84.71(1)Â°, V = 521.2(1) Ã 3, Z = 1, Dcalc = 3.312 g/cm3 was refined to Robs= 5.29 %. The atomic arrangement in lindackerite is very similar to that of chudobaite and geigerite. There are three cationic positions, two As and 15 oxygen atoms. The bond-valence calculation reveals that one oxygen position represents OH group and 7 others water molecules. The substituting Co and Ni atoms enter presumably the special position at Â½, 0, 0, denoted as M. Of other two positions Cu1 is five-coordinated in configuration of square pyramid, whereas Cu2 is octahedrally coordinated. Edge-sharing Cu1 pyramids and Cu2 octahedra form infinite bands parallel to . The adjacent bands are linked together by two kinds of Astetrahedra. As a result a layer parallel to (001) is formed. The adjacent layers are connected via M atoms. In addition, the M position is surrounded by eight half-occupied water molecules (Ow31-Ow34) in four independent positions. This arrangement can be interpreted as two interpenetrating octahedra (with common corners shared with As2 tetrahedra) turned by ~45Â°. In chudobaite and geigerite only one of these alternative octahedra exists and respective positions are fully occupied. One "zeolitic" water molecule Ow1 is located in the interlayer space and is half-occupied. Of other two water molecules Ow4 forms one of apices of the Cu2 octahedron, and Ow2 is located near the base of the Cu1 pyramid, but is rather distant (2.79(1) Ã ) to complete octahedral coordination.