High-Pressure Crystal Chemistry of Earth Materials

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Prewitt9973018Research will focus on minerals believed to occur in the Earth's upper mantle and transition zone, but will also involve studies of relevant phases that provide important crystal chemical information. We will study the effects of disorder on equations of state of isomorphs of mantle phases, including silicate spinels, Mg-Fe pyroxenes, Mg-Fe olivines, and Mg-Fe phase B, as well as Fe3+ and Al-bearing high-pressure phases, in order to quantify differences between isostructural and equilibrium equations of state. We will continue our analysis of the dense, hydrous silicates, specifically the effect of adding Fe2+, Fe3+, Al, Ca, Na, and K to explore mineral compositions more relevant to mantle mineralogy. Structural crystallography is undergoing a revolution initiated by the introduction of new x-ray diffractometers coupled with CCD detectors for three-dimensional recording of diffraction patterns. A new Bruker diffractometer with a CCD detector purchased with support from NSF and the Keck Foundation, will enable us to measure full three-dimensional diffraction patterns of very small crystals, determine the nature of a range of defects affecting crystal properties, and collect data rapidly at a series of increasing/decreasing pressures and/or temperatures. This and other equipment at the Geophysical Laboratory is available to investigators from other institutions who want to conduct crystallographic experiments, especially at high pressures and temperatures