Calcite undergoes a phase transition at 1260 K, which appears to involve the onset of orientational disorder of the carbonate molecular ions.
Full credit is due to members of Team Calcite: Mark Harris, Mark Hagen, Ian Swainson, and Steve Payne.
Our papers on this subject include (in reverse chronological order):
S J Payne, M J Harris, M E Hagen and M T Dove, "A neutron diffraction study of the order--disorder phase transition in sodium nitrate". Journal of Physics: Condensed Matter (submitted)
M T Dove, I P Swainson, B M Powell and D C Tennant, "Structural studies of the orientational order--disorder phase transition in calcite, CaCO3". Physics and Chemistry of Minerals (submitted, awaiting corrections)
M T Dove, M E Hagen, M J Harris, B M Powell, U Steigenberger and B Winkler, "Anomalous inelastic neutron scattering from calcite". Journal of Physics: Condensed Matter 4, 2761-2774, 1992.
M Hagen, M T Dove, M J Harris, U Steigenberger and B M Powell, "Orientational order-disorder phase transition in calcite". Physica B 180-181, 276-278, 1992.
M T Dove, B Winkler, M Leslie, M J Harris and E Salje, "A new interatomic potential model for calcite". American Mineralogist 77, 244-250, 1992.
M T Dove and B M Powell, "Neutron diffraction study of the tricritical orientational order/disorder phase transition in calcite at 1260 K". Physics and Chemistry of Minerals 16, 503-507, 1989.
Link back to ...