Die„geordnete gemittelte“ Kristallstruktur von Parascholzit. Zur Dimorphie von CaZn2(PO4)2 · 2H2O, Parascholzit – Scholzit

Abstract

Abstract Parascholzite (SG: I2/c, a = 17.186(6) Å, b = = 7.413(3) Å, c = 6.663(2) Å, β = 95.39(3)°, Z = 4, ϱ = = 3.12g/cm3, ϱ = 3.118g/cm3, V = 845(5) Å3, R(F) = = 3.0%) and the idealized substructure of scholzite, SG: Pbcn, a = 17.149(3) Å, b = 7.421(1) Å, c = 6.667(1) Å, Z = 4, are “building unit structures” with layer compositions of [ZnPO4]− 2n and [Ca · 2H2O]2+ n . The respective phase of CaZn2[PO4]2 · 2H2O originates from both the conformation of the crystal water together with the oxygens of the zinc phosphate and two alternatives of octahedrally coordinated interstices for the Ca2+-ions. The prediction of the parascholzite structure, which had been made earlier with the aid of order-disorder considerations (Taxer, 1992), was confirmed experimentally.