Structural and mechanical properties of dolomite rock under high pressure conditions: A first-principles study

Abstract

The structural behaviour of carbonate minerals under lower mantle pressures, experimentally investigated by means of X-ray diffraction and infrared spectra measurements can be interpreted and difficulties surmounted by first principles quantum mechanical simulations based on density functional theory (DFT). This work is devoted to structural and mechanical properties of CaMg(CO3)2-dolomite mineral. From Birch-Murnaghan equation of state (BM-EoS) applied to the energy-volume data of the dolomite polymorph, we obtain a bulk modulus of 93.7GPa with a pressure derivative of 4.7, which show suitable agreement with experimental data. Under hydrostatic pressure the mineral system shows an anisotropic compression behaviour and is found to be more compressible in the z direction. The investigation of dolomite mineral structural phase stability under hydrostatic pressure has confirmed previously range-determined but still debated values of structural phase transition. Two phases transitions were encountered when increasing pressure. The first one occurring from dolomite to the orthorhombic calcite-III-like structure was predicted at ∼34GPa; and the second one between the calcite III and the aragonite II at ∼52.5GPa. This approach overestimates the transition pressure value when confronted to experimental findings. On the other hand the mechanical behaviour of this mineral under ambient and high pressure conditions was studied. To this end we used a stress-strain ab initio based model to calculate the elastic constants of CaMg(CO3)2-dolomite. Based on the trigonal symmetry (space group R3) we found 196.6, 64.4, 54.7, 22.4, 110 and 41.6GPa for C11, C12, C13, C14, C33 and C44, respectively. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.