Hydrous Components in Nominally Anhydrous Crustal Minerals

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RossmanEAR-0125767Many minerals that are usually formulated as anhydrous actually contain low concentrations of water or hydroxide bound in distinct sites in their structure. These components influence the properties of the host phase to an extent that is far disproportionate to their actual concentrations, and together, constitute a globally significant reservoir of hydrogen in planet Earth. Our research program is directed at 1) characterizing the chemical form and concentrations of these components in natural minerals and related synthetic materials, 2) relating the hydrous components to other physical and chemical properties of the host phases, and 3) exploring the significance of the hydrous components to the terrestrial geologic system. We select naturally occurring minerals from several geologic occurrences and characterize their hydrous components with a variety of spectroscopic probes. One major objective is to determine the quantitative amount of the hydrous components in the host phases. The general characterization of hydrous components in minerals provides basic information about the global water reservoir contained in minerals systems and provides information relevant to the entry and role of hydrogen into technological products (synthetic minerals and related structures) used in a variety of industries. The absolute calibration data is needed to constrain the quantitative amount of hydrogen in the various mineral reservoirs, an important parameter in evaluating the role and transport of volatiles in the Earth's systems. We ultimately expect to be able to prepare general calibrations for major groups of minerals found in the earth's crust.The content of these components in anhydrous minerals is potentially a useful indicator of fluid history or fluid variation within a geological system. We will work to establish the extent and conditions under which anhydrous minerals preserve a record of water activity in rock by investigating the variation of OH in anhydrous minerals in well-studied geological environments that have experienced inhomogeneous fluid conditions. Our results will be compared to oxygen isotope systematics that record fluid history in the same mineral or rock. Through detailed studies, we will gain insight into factors such as oxygen fugacity that could modify the retention of OH and H2O in anhydrous mineral structures.