In situ X-ray diffraction of aragonite and dolomite at high pressure and high temperature; evidence for dolomite breakdown to aragonite and magnesite

The crystal data and stability of calcite III at high pressures based on single-crystal X-ray experiments

“…Redfern, 2000, for details), which is less than the transition pressure from calcite to calcite II. The densities of aragonite at 2.0 and 4.0 GPa are obtained to be 3.01 and 3.08 g/cm 3 (Martinez et al, 1996), respectively, which are substantially higher than those of calcite III, 2.93 and 3.03 g/cm 3 , respectively at these pressures, as obtained here. Therefore, the present study indicates that calcite III, as well as calcite II, is metastable with respect to aragonite at high pressures.…”

“…This is contrary to a general trend that a denser high pressure phase is less compressible than its lower pressure phase. However, we note aragonite, a high pressure phase of calcite, is again more compressible than calcite; K0 = 65.4(5) GPa for aragonite (Martinez et al, 1996) and K0 = 73 76 GPa for calcite (Chen et al, 2001, and references therein).…”

Experimental calibration of clumped isotope reordering in dolomite

“…The type locality for optical-quality dolomite (Lugli et al, 2000), Eugui dolomite is compositionally homogeneous, near-perfectly stoichiometric, well-ordered, and largely free of structural defects (Barber et al, 1981;Navrotsky and Capobianco, 1987;Reeder and Nakajima, 1982;Reeder and Wenk, 1983). It has been the starting material for a large number of investigations of dolomite crystallinity, thermal stability, deformation and dissolution rates (Barber et al, 1981;Chai and Navrotsky, 1996;Martinez et al, 1996;Reeder and Markgraf, 1986;Urosevic et al, 2012), and a reference standard against which the physical and chemical properties of sedimentary and saddle dolomites are compared (Barber et al, 1985;Jones et al, 2001). Given the paucity of ordered, stochiometric, megacrystic dolomite in nature, and the utility of direct comparison of ∆47 reordering rates to other properties of this well-characterized sample, we suggest that the Eugui dolomite is an appropriate material for these experiments, provided its initial ∆47 composition is sufficiently uniform and resolved from the equilibrium high-temperature limit.…”

Influence of pressure and temperature on the electrical conductivity of dolomite

“…The measurements of the electrical conductivity were performed at pressures ≤6 GPa, because dolomite decomposes into magnesite and aragonite at high pressures (Liu and Lin 1995;Martinez et al 1996;Sato and Katsura 2001;Luth 2001;Shirasaka et al 2002;Buob et al 2006). Figure 2 shows a representative complex impedance curve from a sample of dolomite.…”