Crystal structure refinements of magnesite, calcite, rhodochrosite, siderite, smithonite, and dolomite, with discussion of some aspects of the stereochemistry of calcite type carbonates

Abstract

Abstract The crystal structures of magnesite, calcite, rhodochrosite, siderite, smithonite and dolomite were refined by standard single crystal X-ray methods using diffraction data up to sin[unk]/λ = 1.0 Å−1. The C – O bond lengths are essentially the same. Attention is drawn to short O – O contacts (2.85 Å in both magnesite and smithonite) outside the coordination figures. The MeO6 octahedra are always elongated parallel [00.1]; the distortion is not a monotone function of the Me – O distance. The approximation of four point charges for the [CO3]2− ion for calcite gives good agreement between observation and classical electrostatic calculation when charges of 1 + for carbon and 1 − for oxygen are used.