3D MICROSTRUCTURAL AND MAGNETIC ASSESSMENT OF CRYSTALLITES IN WESTERN NORTH AMERICAN OBSIDIANS

Nano- and micro-lites, oft present crystallites in amorphous matrices, are central to understanding magma behavior. While typically only occupying small volume fractions within a melt (often <1%), they can have an outsized impact on viscosity, and therefore, explosivity. These crystallites can also provide a record of magma behavior. Several obsidian samples containing nanolites and/or microlites from across Western North America are investigated with X-ray nano-Computed Tomography (nano-CT) for 3D structural visualization, X-ray Diffraction (XRD) for crystalline phase identification, Vibrating Sample Magnetometry (VSM) for characterization of magnetic properties, and Raman spectroscopy for glass structure. Specifically, samples from Glass Butte, Oregon, Newberry Crater, Oregon, Panum Volcano, California, and Mexico, are examined. This combination of techniques enables unique examination of crystal morphologies, such as flow banding and unusual curled microstructures. Further, origin of colors in a polychrome sample is assigned to specific microstructural features by correlating imaging techniques. In addition, since many of the examined crystallites are iron oxides, magnetic properties are additionally investigated, such as the presence of wasp-waisted hysteresis curves. A comparison of varied specimens characterized with these unique methods is provided and the resulting insights into obsidians discussed.