Original paper

Crystal structures of three CaSeO4 polymorphs and their mineralogical relationships

Pristacz, H.; Talla, D.; Preuschl, F.; Giester, G.; Wildner, M.

Abstract

Three polymorphs of anhydrous calcium selenate CaSeO4 have been synthesized; the orthorhombic as well as the monoclinic polymorph were prepared at 210 °C; crystals of tetragonal CaSeO4 were grown at 70 °C. Based on single crystal X-ray diffraction data the structure of the orthorhombic compound was solved and refined in space group Cmca [a = 7.192(1), b = 14.404(2), c = 6.398(1) Å, V = 662.8 Å3, Z = 8 to R1 = 2.0 %, wR2 = 5.5 %]. It belongs to a new structure type with close resemblance to zircon and anhydrite. The structure of monoclinic CaSeO4 is isotypic with monazite and was refined in space group P21/n[a = 6.860(1), b = 7.086(1), c = 6.692(1) Å, ß = 104.21(1)°, V = 315.3 Å3, Z = 4; R1 = 2.6 %, wR2 = 5.2 %]. The tetragonal modification, refined in space group I41/a, (a = 5.054(1), c = 11.678(2) Å, V = 298.3 Å3, Z = 4; R1 = 1.6 %, wR2 = 4.1 %) represents a scheelite structure type. In addition, structure relationships within A[8]X[4]O4 representatives are emphasized.

Keywords

anhydritea[8]x[4]o4caseo4crystal structurehydrothermal synthesismonazitescheelitezircon