Scanning Microscopy


In studies involving radiometric, isotopic, or chemical analyses of authigenic potassium feldspar (K-feldspar), suitable samples are usually available only in the form of authigenic overgrowths on detrital igneous or metamorphic grains. The analysis of these mixtures often requires a measurement of the relative proportion of each component. To address this need, a technique has been developed which utilizes backscattered-electron (BSE) and cathodoluminescence (CL) detectors together with an image analyzer to quantify the relative proportions of authigenic and detrital K-feldspar in monomineralic separates. Authigenic (low temperature) K-feldspar overgrowths are distinguished from high temperature K-feldspar cores by their lack of luminescence. Computer analysis of BSE and CL images of polished grain mounts is used to compute a ratio of the area of luminescing (high-temperature) cores to the area of the total population of grains. Measurements made on synthetic standards indicate that area ratios determined in this manner are equivalent to true volume ratios, and that accuracies on the order of 8 percent (relative error) are obtainable.

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