Structural Changes in Minerals and their Effect on Intrinsic Properties

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My LONG-TERM RESEARCH PROGRAM examines mineral behaviour (physical, mechanical, thermodynamic, elastic, and chemical properties) as a function of pressure (P), temperature (T), composition (X), and time (t), that is, P-T-X-t conditions, which is based on the arrangement of atoms in the crystal. Understanding mineral behaviour is essential for providing realistic models for Earth processes because mineral properties are governed by the arrangement of atoms. My research program attempts to answer questions such as: why do solid materials have the composition, structure, and the properties that they exhibit? How do these properties change under different P and T conditions? How does the ordering of atoms in a structure change in response to P-T-X-t? What are the effects of order-disorder on intrinsic or internal properties, e.g., density? To answer these questions, it is necessary to determine the atomic structures of minerals using a multi-disciplinary approach. We use various in situ experimental techniques to investigate the processes that govern mineral stabilities and properties under ambient and non-ambient (different P and T) conditions, including X and t, and to apply the results to Mineral Physics and Earth processes. My research program is based on physical chemistry and diffraction physics using experimental techniques in laboratories in addition to performing innovative research at synchrotron and neutron facilities, where I am an established researcher. We have successfully characterized several mineral groups under varying P-T-X-t conditions and here we examine the garnet-group minerals. My SHORT-TERM OBJECTIVES FOR THE NEXT 5 YRS are to examine the behaviour of garnet-group minerals with P-T-X-t. Garnets are important because they occur over a range of P-T-X-t conditions and they preserve important records of igneous and metamorphic processes. Garnets have important technological properties (e.g., lasers and automotive batteries) and some form natural "thin films", which affect their properties. "Thin films" occur as compositional zoning, which is well known in feldspars and about 75 other minerals, so our work will have implications for numerous minerals. Zones in garnets have slightly different chemical and structural parameters. Cation substitution and zoning in garnet solid solutions must be considered in their thermodynamic behaviour and their effective use in geothermometry, geobarometry, and geochronology. Moreover, order-disorder processes affect seismic velocities and are needed for geophysical models. We will study multiple phases, anomalous birefringence, zoning, cation order, diffusion, and seismic velocities in garnets. This work will provide excellent training for at least 14 new students. They will learn important techniques to solve problems in the fields of mineralogy, crystallography, and materials science.