Abstract

A method is described that facilitates rapid correlative light and scanning electron microscopic observations of mineral grains. The grains are fixed on a film of epoxy resin on a standard microscope slide so that successive treatments can be performed on individual grains. Specific grains can be located by the coordinates on a mechanical stage on the light microscope, studied by various optical techniques, the slide transferred to a modified scanning electron microscope stage, and the grains readily relocated. Micrographs of a microcline grain and an opal-chalcedony grain are used to demonstrate the capabilities of light microscopy (including polarized light techniques, differential interference contrast, and phase contrast) and scanning electron microscopy in studying the form and surface features of the grains. In particular it was found that the conductive coating of Pt-Pd (or Au) had no apparent effect on the optical properties of the minerals. The scanning electron microscope is a powerful tool for resolving fine surface detail in minerals particularly when coupled with the polarizing microscope for rapid, direct specimen identification. Phase contrast permits better resolution of grain borders, cleavage traces, fracture zones and crystal domains than other light optics but is only slightly superior to differential interference contrast in this aspect. One limitation of the differential interference contrast method is that optical relief may reflect variation in mineral composition rather than geometric thickness gradients.

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