Crystal Chemistry of Some Silicates and Carbonates

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Three principle direction of research will be followed: 1) Reaction mechanisms and diffusional processes at high pressures, and the role of protons will be examined for the most part by measuring rate of oxygen isotope exchange under different conditions; 2) Determination of oxygen isotope fractionation factors in minerals of interest, in part in conjunction with the above; 3) Order-disorder phenomena in silicates, and synthesis of intermediate states of Al/Si order in albite followed by solution calorimetry at high temperatures for information on the energetics of the order-disorder process. This will involve the effect of Al-concentration on diffusion and reaction rates, the varying availability of hydrogen (protons), and examination of rates of exchange in minerals with variation of 4 and 6 Al coordinations, all to be oxygen exchanged with CO2 or CaCO3. Specifically studied will be andalusite, sillimanite and kyanite, the plagioclase series, the melilite series, and the pair beryl- cordierite. Fractionation factors will also be determined. Calorimetric work will be carried out on albites (NaAlSi3O8) synthesized at high pressures with controlled and variable degrees of Al/Si order to obtain data on the energetics of the order-disorder process.