THE CRYSTAL STRUCTURE OF AN ANTHROPOGENIC Cu–K–Na–HYDRO-HYDROXYL–CARBONATE–CHLORIDE FROM JOHANNGEORGENSTADT, SAXONY, GERMANY

The Cu–K–Na–hydro-hydroxyl–carbonate–chloride, K5 Na2 Cu24 (CO3)16 Cl3 (OH)20 (H2O)12, has been found on a museum specimen labeled Johanngeorgenstadt, Saxony, Germany. It occurs as blue transparent cubes 0.2 mm across on massive maucherite, and the unusual mineralogical and geochemical associations suggest that this phase may be of anthropogenic origin. The crystal structure of this material, cubic, space group F23, a 15.463(1) Å, V 3697.5(1.6) Å3, Z = 2, was solved by direct methods and refined to an R1 index of 4.3% based on 409 observed (> 4 F) reflections measured with MoK X-radiation. Electron-microprobe analysis gave the following empirical formula: K6.97 Na1.22 (Cu22.46 Ni0.12 As0.15) 22.73 C16.57 O48 (OH)20 (H2O)12 Cl1.97 based on 83 (Cl + O) apfu. There is one Cu site surrounded by three O atoms and two (OH) groups, with = 2.025 Å. There are two alkali sites, the Na site in regular octahedral coordination by six (H2O) groups, with = 2.414 Å, and the K site coordinated by three oxygen atoms, 1.5 (OH) groups, three (H2O) groups and one Cl atom, with = 2.998 Å. There are two C sites, each coordinated by three oxygen atoms, with = 1.283 and 1.245 Å, respectively. There are two types of Cl sites: Cl(1) is a ligand for K, and Cl(2) receives four hydrogen bonds from OH groups in a tetrahedral arrangement. Three {Cu2+ O3 (OH)2} polyhedra link through common edges to form a trimeric [Cu3 O6 (OH)4] cluster. Four of these clusters connect through common vertices to form a 12-membered cluster of point symmetry 23. In this cluster, every three trimeric clusters are linked by a (CO3) group, resulting in a [Cu12 C4 O24 (OH)8] cluster. These large clusters link through (CO3) groups to form cages that accommodate the Na, K and Cl(2) sites. There is extensive hydrogen bonding between (OH) groups and Cl atoms and between (H2O) groups and O atoms.