Heat capacity measurements of sub-milligram quantities of mantle minerals

Knowledge of heat capacities and standard entropies of mantle minerals is necessary for thermodynamic modeling of high P-T equilibria. However many of these materials can only be prepared in milligram quantities in a multianvil apparatus or in microgram quantities in a diamond anvil cell. This eliminates traditional adiabatic calorimetry techniques for Cp measurements. Our microcalorimeters have been used to successfully measure thin films, multilayers, and magnetic single crystals. Using these ``calorimeters on a chip'', we are measuring the heat capacity of the Fe$_{2}$SiO$_{4}$ olivine and spinel polymorphs from 2 K to room temperature. This will provide a direct measurement of the entropy of the olivine-spinel transition and will uncover possible magnetic phase transitions at low temperature in the spinel phase. We would like to thank the DOE for funding this research.