Anisotropic thermal expansion of calcite at high pressures; an in situ X-ray diffraction study in a hydrothermal diamond-anvil cell

Abstract

Lattice parameters of calcite were measured at simultaneous high pressures and temperatures up to 10 kbar and 500°C. Samples of Solnhofen limestone and distilled, deionized water were loaded in a hydrothermal diamond-anvil cell. In situ energy-dispersive X-ray diffraction was used to determine lattice parameters along five H20 isochores with densities of 1.040, 0.964, 0.760, 0.670, and 0.595 glcm3from 30 to 500°C; these densities correspond to the ice-melting temperature of -7.7 °C and the liquid-vapor homogenization temperatures 92.4,274.5, 318.9, and 344.6 °C, respectively. In addition, data along the P axis were collected by hydrostatic compression at room temperature and along the T axis by heating at atmospheric pressure. Our results show that anisotropic thermal expansion of calcite continues up to 10 kbar, therefore making it a good double internal X-ray standard. Both a and c lattice parameters are fitted to second-order polynomials of pressure, temperature, and a cross term.