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Scanning Microscopy

Abstract

Several new applications of cathodoluminescence (CL) have been developed during the last few years, including: combined CL imaging and/or spectroscopy and CL observations of carbonates previously considered to be non-luminescent or of minor interest. Basically, two previously unstudied types of carbonates were investigated: marbles, and recent shells. From numerous classical white marble samples, cathodomicrofacies were defined and described. A single cathodomicrofacies is generally characteristic of a given area. This finding permits identification of the source of white marbles and has been successfully applied to ancient marbles from different collections. Despite the well established idea that CL in biogenic carbonates is due solely to diagenetic phenomena, most recent biogenic carbonates show growth zonations which are enhanced under CL. This phenomenon is independent of shell mineralogy (calcite or aragonite), habitat (marine or fresh water), life mode or environment. Thus, the idea that unaltered shells are non-luminescent is contradicted. These observations have important implications for future studies of geochemical paleo-oceanic reconstructions as well as ontogenetic researches. Low-luminescing calcites are good examples of blue CL emission in natural calcite. Preliminary results are shown. One of the major advantages of using CL is that the original structure and texture of the sample is observable and there is no averaging of chemical information. CL gives in situ information on intrinsic (host lattice) luminescence emissions and the pattern of trace elements in the crystals. To quantitatively interpret the CL image, a non-destructive in situ method of chemical analysis is needed. Further progress in CL is likely to include quantitative spectroscopy and in situ chemical analyses.

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