POSITIONAL DISORDER OF OXYGEN IN GARNET: THE CRYSTAL-STRUCTURE REFINEMENT OF SCHORLOMITE

RONALD C. PETERSON
Department of Geological Sciences, Queen's University, Kingston, Ontario K7L 3N6

ANDREW J. LOCOCK and ROBERT W. LUTH
Department of Geology, University of Alberta, Edmonton, Alberta T6G 2E3

Abstract

The structure of a crystal of schorlomite garnet with composition {Ca2.87Mg0.10Na0.04} [Ti1.06Fe3+0.63Al0.14Fe2+0.06Zr0.04Mg0.04Mn0.03V0.01](Si2.35Fe3+0.34Fe2+0.31)O12, and an a parameter of 12.157(3) Å, has been refined using MoK X-ray- diffraction data to an Rw of 0.042. The oxygen atom in the structure is modeled by a split isotropic position, which results from significant occupancy of the tetrahedral site by iron. Lengths of bonds between tetrahedrally coordinated cations and the two oxygen atoms are consistent with silicon- oxygen and iron-oxygen distances observed in other garnet structures.

Keywords: schorlomite, garnet, structure refinement.