The chemistry, mineralogy and temperature of Earth’s interior are the most fundamental properties of our planet, but because direct access is limited we must infer them from seismological observations. This requires knowledge of the properties for Earth's minerals at mantle P&T. Unfortunately, experimental measurements are sparse, such that finite-strain extrapolations or ab-initio calculations are required. However, the accuracy of neither method is demonstrated, and no data to test these techniques exists. Here we will measure the thermal expansivity of forsterite and periclase (two abundant mantle minerals) to temperatures of the mantle adiabat. This will allow us to benchmark the accuracy of current approaches and build correction routines if required, to improve the accuracy of calcualtions and/or extrapolations.

The chemistry, mineralogy and temperature of Earth’s interior are the most fundamental properties of our planet, but because direct access is limited we must infer them from seismological observations. This requires knowledge of the properties for Earth's minerals at mantle P&T. Unfortunately, experimental measurements are sparse, such that finite-strain extrapolations or ab-initio calculations are required. However, the accuracy of neither method is demonstrated, and no data to test these techniques exists. Here we will measure the thermal expansivity of forsterite and periclase (two abundant mantle minerals) to temperatures of the mantle adiabat. This will allow us to benchmark the accuracy of current approaches and build correction routines if required, to improve the accuracy of calcualtions and/or extrapolations.

Olivines - in particular the solid-solution between forsterite (Mg2SiO4) and fayalite (Fe2SiO4) - are important rock-forming minerals on Earth, also occurring in meteorites and interstellar dust. Olivines form the major component of Earth's upper mantle and the point at which their structure becomes unstable with respect to denser minerals marks the upper boundary of the transition zone between the upper and lower mantle. The thermal expansion of fayalite (Fe2SiO4) is unusual and not well understood at present. The expansion coefficients of two of the axes of the crystal have a "normal" temperature dependence, tending to zero as T goes to 0 K and becoming almost constant at high T; however, for the other axis the expansion coefficient is roughly constant between about 80 K and 1100 K. The purpose of our experiment is to understand the structural basis of these differences in behaviour