Statistics – Computation
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.v42e..07g&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #V42E-07
Statistics
Computation
3630 Experimental Mineralogy And Petrology, 3694 Instruments And Techniques
Scientific paper
The Earth, as well as other solid planets and meteorites, is largely made up of solid-solution minerals. An understanding of their microscopic, mesoscopic and macroscopic properties and their behavior under different P-T conditions is a challenge for all disciplines concerned with the solid state. A major goal of mineral physics is to investigate how microscopic and mesoscopic properties control or affect the thermodynamic and bulk physical properties of minerals. Advances in different spectroscopic methods such as IR, Mössbauer, Raman, NMR, and X-ray and optical absorption make this possible. In addition, developments in computational methods are increasing rapidly and allow detailed microscopic properties to be investigated. For example, 29Si NMR investigations are showing that many silicate solid solutions (e.g. pyroxene, garnet, feldspar) are characterized by short-range cation order. Previously, the question of short-range order had largely been ignored in thermodynamic modeling studies because its determination by diffraction methods is very difficult. Raman and IR spectra are being used to characterize structural heterogeneity and thus lattice strain over different correlation lengths. Lattice strain, resulting from size differences of mixing atoms, is largely responsible for nonideal thermodynamic behavior in the volume and enthalpy of mixing for most silicate solid solutions. Chemical effects such as crystal field stabilization energies can also play role in affecting thermodynamic properties, but they are generally second-order compared to strain. Local-site relaxation and localized strain properties in solid solutions can also be studied with element specific methods such as XAS or optical absorption spectroscopy. Third generation synchrotrons allow XAS studies even at the trace element level in minerals. The aluminosilicate garnet and the Na-K feldspar solid solutions have received much structural and thermodynamic study using many different experimental and computational methods. Both systems are characterized by positive excess mixing with respect to volume, enthalpy and vibrational entropy. The thermodynamic properties can be explained partly by their microscopic structural properties. These two solid-solution systems will be addressed and recent experimental results, largely spectroscopic based, will be presented and discussed with regards to their solid-solution behavior.
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