A comparison of the clinopyroxene compounds CaZnSi2O6 and CaZnGe2O6.

Single crystals of CaZnSi2O6 (calcium zinc silicate) and CaZnGe2O6 (calcium zinc germanate) were synthesized at 1623 K and 2.5 GPa by slow cooling of the melts from 1473 K. Structure solution using Patterson methods revealed the two compounds to be isomorphous and thus isostructural. They adopt the clinopyroxene structure type with space group C2/c. The substitution of Ge4+ for Si4+ increases the distortion of the tetrahedra and octahedra. The increased size of the tetrahedral GeO4 chain is mainly compensated by (i) increasing the kinking of the tetrahedral chain and (ii) lengthening the Zn-O bonds.