Thermal Expansion of Synthetic Aragonite Condensed Review of Elastic Properties

Samples of pure aragonite are synthesized by precipitation from aqueous solution and used to determine the heat capacity and temperature dependence of the unit cell parameters in the temperature range 291–700 K. The X-ray diffraction powder diagram at room temperature is refined in space group Pnma and resulted in the cell parameters a=5.7444(8) ?, b=4.9620 (4) A, c=7.9700(6) A, and V=227.17(3) A3. TRXD allows the study of the thermal expansion of the lattice up to the phase transition to the stable calcite which occurs at 723 K. Anisotropic expansion coefficients are computed in the temperature ranges 291–700 K and 800–900 K for aragonite and calcite, respectively. From heat capacity measurements and high pressure compressibility data from the literature, some elastic coefficients of aragonite and calcite, particularly those of the Grüneisen type, are reexamined.