Mineralogical Applications of Transmission Electron Microscopy and Energy-Filtered TEM

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VeblenEAR-0073955This proposal is a renewal of a previous research program that involved applications of transmission electron microscopy (TEM) and ancillary techniques to problems important to the fields of mineralogy, petrology, and geochemistry. In this renewal, several diverse projects are proposed with an underlying thread of trying to understand the crystal chemistry of minerals and their reactions at the sub-nanometer scale. These projects will make use of a new NSF-supported, 300-kV TEM with a field-emission gun, an instrument that has excellent resolution for normal high-resolution TEM experiments and has revolutionized our chemical capabilities. The primary emphasis of the work proposed will be the exploration of how these new analytical capabilities can be applied to mineralogy and geology, as applications of this technique to the earth sciences so far have been largely unexplored. It is proposed to attempt direct chemical analysis of a number of mineral microstructures that are in the size range of less than one to a few unit cells. These include stacking faults, twin planes, and antiphase boundaries in pyroxenes and other minerals; the C domains in calcian dolomite; the fine-scale chemical modulations associated with spinodal decompositions in pyroxenes and feldspars; and Guinier-Preston zones that form during kinetically arrested exsolution in chain silicates. In addition, efforts to achieve quantification using these new analytical methods will be continued. Other projects to be pursued include explorations of structural disorder and chemical variation in newly synthesized, Na- and K-bearing, high-pressure pyriboles that contain alternating single and double silicate chains; of possible relationships between chemical composition and superstructures in the sulfides bornite and digenite; of order-disorder relationships in hibonite and other minerals of the magnetoplumbite group.