Magnetic susceptibility, Meteorites -- Density, Meteorites -- Magnetic properties, Meteorites -- Properties, Porosity
The measurement of meteorite physical properties (i.e. density, porosity, magnetic susceptibility) supplements detailed chemical and isotopic analyses for small samples (thin sections or ~300 mg portions) by providing whole-rock data for samples massing in the tens of grams. With the advent of fast, non-destructive and non-contaminating measurement techniques including helium ideal-gas pycnometry for grain density, the Archimedean ―glass bead‖ method for bulk density and (with grain density) porosity, and the use of low-field magnetometry for magnetic susceptibility, all of which rely on compact and portable equipment, this has enabled a comprehensive survey of these physical properties for a wide variety of meteorites. This dissertation reports on the results of that survey, which spanned seven major museum and university meteorite collections as well as the Vatican collection. Bulk and grain densities, porosities and magnetic susceptibilities are reported for 1228 stones from 664 separate meteorites, including several rare meteorite types that are underrepresented in previous studies. Summarized here are data for chondrites (carbonaceous, ordinary and enstatite) and stony achondrites. Several new findings have resulted from this study. From the use of a ―weathering modulus‖ based on grain density and magnetic susceptibility to quantify weathering in finds, it is observed that the degree of weathering of ordinary chondrites is dependent on their initial porosity, which becomes reduced to less than ~8% for all finds, but for enstatite chondrites iii weathering actually increases porosity. Grain density and magnetic susceptibility, which have been shown to distinguish H, L and LL ordinary chondrites, also may distinguish shergottites, nakhlites and chassignites from each other, but the two groups of enstatite chondrites (EH and EL) remain indistinguishable in these properties. H chondrite finds exhibit a slight negative trend in porosity with increasing petrographic type, and all chondrite falls together exhibit a pronounced negative trend in porosity spanning all petrographic types. The overall trend corresponds roughly to a positive trend in porosities with respect to both degree of oxidation and percentage of matrix. It also corresponds to the macroporosities of analogous asteroids. These traits constrain models of conditions in the solar nebula and the formation of chondrite parentbody precursors.
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Doctor of Philosophy (Ph.D.)
College of Sciences
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Dissertations, Academic -- Sciences, Sciences -- Dissertations, Academic
Macke, Robert J., "Survey Of Meteorite Physical Properties Density, Porosity And Magnetic Susceptibility" (2010). Electronic Theses and Dissertations. 1638.