Abstract
Structural parameters have been refined from X-ray intensity data for a stoichiometric dolomite single crystal at 24, 200, 400, and 600°C. Both a rigid-body model and a conventional anisotropic thermal model were used for refinements, yielding nearly identical values for temperature factors and residuals. This attests to the suitability of the rigid-body model over the temperature range studied.
Thermal expansion of a and c are similar to that of magnesite but markedly different from that of calcite. The Ca and Mg octahedra expand more rapidly than those in calcite and magnesite, respectively, and also differently. The Ca octahedron shows no increase in distortion with temperature as it does in calcite, and yet the Mg octahedron does, which contrasts with its behavior in magnesite. Rigid-body libration of the CO3 group is intermediate in magnitude between that in calcite and magnesite, and neither rotation around the threefold axis nor out-of-plane tilting is dominant. Expansion of the libration-corrected C-O bond length is nearly identical to that in magnesite and substantially less than that in calcite.
No evidence of cation disorder is found throughout the temperature range studied.
