The crystal structure is the most fundamental property of a mineral. The structure along with composition determines the mineral?s physical and chemical behavior. Under high-pressure conditions of Earth?s deep interior, minerals often undergo phase transformations to new, denser crystal structures. The purpose of this project is to use advanced experimental techniques to study the evolution of crystal structures under high pressures for some of the most abundant minerals of the Earth?s upper mantle. Pressure will be generated using a diamond anvil cell which is a device in which the sample is squeezed between the tips of small diamonds. The crystal structure is probed with a powerful X-ray beam from a synchrotron radiation facility. Minerals to be studied include the major minerals of Earth?s upper mantle: olivine, pyroxene, and garnet. The work will lead to the discovery of new crystal structures which are relevant for understanding the high-pressure behavior of these important Earth materials.

We will use synchrotron-based single-crystal X-ray diffraction techniques to examine the crystal structure and equation of state of mantle minerals to pressures up to 1 Mbar (100 GPa). Compared to more standard powder X-ray diffraction techniques, single-crystal methods have many advantages. Initially, we have collected synchrotron-based single-crystal X-ray diffraction on synthetic olivine, Mg2SiO4, and observed a previously unknown phase transition at 50 GPa. By using small crystals in a nearly isotropic helium pressure-transmitting medium, it is possible to retain single crystals across phase transitions. This opens the opportunity to obtain precise constraints on the lattice parameters, equation of state, and crystal structure of high-pressure phases. We will also work on extending capabilities to simultaneous high P-T conditions using external and laser heating techniques. The application of new single-crystal X-ray techniques has the potential to be a major advance in high-pressure research.

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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Jennifer Wade
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Princeton University
United States
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