Internal pressure in annealed biogenic aragonite

Abstract

The thermal expansion of biomineral aragonite (CaCO₃) was studied by in-situsynchrotron radiation (SR) diffraction in both pulverized and non-pulverized samples. The thermal expansion of biogenic aragonite depends on the sample form. Pulverized biomineral aragonite samples show the same thermal expansion as the reference geological aragonite. Biomineral aragonite samples studied en-bloc (non-pulverized) show smaller thermal expansion coefficients as compared with the reference geological aragonite. The observed difference is attributed to the pressure exerted by the heated organic inclusions trapped in the lattice of the biomineral samples studied en-bloc. The estimated pressure values are of the order of 200–350 MPa at temperatures ranging from 400 to 500 °C. The pressure values are different for the main crystallographic directions. The structural phase transition from aragonite to calcite is observed at different temperatures for pulverized biomineral 280 °C, biomineral en-bloc 360 °C and geological 450 °C aragonite samples.