Phase Equilibria and Crystal-Chemistry of Some Calcic Amphiboles

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9316079 Jenkins This project will examine both macroscopic and microscopic aspects of the substitution of Al into calcic amphiboles in response to variations in the pressure, temperature, and compositional conditions of formation. Variations in the Al content of tremolitic amphibole should provide a wider data base for testing and refining the thermodynamic mixing properties of amphiboles in the system H2O-CaO-MgO-Al2O3- SiO2. Research on Fe-Tschermak's substitution will seek to quantify the strong correlation observed between Fe2+ and Al and natural calcic amphiboles. The pressure dependency of the actinolite-hornblende miscibility gap will be investigated by examining the volume-composition relationships along the join tremolite-pargasite, which serves as an approximation to the actinolite-hornblende "join". Considerable attention will be devoted to the detailed examination of Al distribution in synthetic amphiboles by using MAS-NMR, IR and XRD Rietveld techniques. This information will facilitate the extraction of thermochemical mixing properties of Al from available data on calcic amphiboles.