Equations of state of mantle minerals from high-pressure diffraction

Abstract

The density and seismic velocities of candidate mantle minerals provide, by comparison with seismic observations of the mantle, constraints on mantle mineralogy. Laboratory measurements of the density of minerals at high pressures can be obtained by a variety of high-pressure diffraction techniques. We review the available experimental techniques paying particular attention to the precision and accuracy with which the density of the mineral can be determined at high pressures, and hence the equation of state determined. We conclude that even with recent advances in powder diffraction techniques the precision is still significantly lower than is available from single-crystal diffraction measurements. We therefore recommend the use of single-crystal data wherever possible as the basis for the calculation of the densities of mineralogical models of the Earth's mantle, supplemented by data obtained by powder diffraction only as a secondary source of data.