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Abstract

Although petrography is an extremely valuable tool for the identification of minerals and their textural interrelations, it is best used (in many cases) in conjunction with other techniques.

Precise mineral determination commonly is aided by staining of thin sections or rock slabs, by X-ray diffraction analysis, or by microprobe examination. Minerals present in small amounts may best be analyzed after separation and concentration using heavy liquids, shaker tables, or other techniques. Likewise, noncarbonate minerals in a carbonate host rock are normally better analyzed in acid-insoluble residues than in thin section. Where detailed understanding of the trace element chemistry of the sediments is essential, X-ray fluorescence, microprobe, atomic absorption, or cathodoluminescence techniques may be applicable.

Commonly, sediments are too fine-grained for adequate examination with the light microscope. The practical limit of resolution of the best light microscopes is in the one to two micrometer (μm) range. Many detrital and authigenic grains such as clays, micritic carbonates, or organic matter fall within or below that size range. Furthermore, because most standard thin sections are about 30 μm thick, a researcher examines 10 to 20 of these small grains stacked on top of one another, with obvious loss of resolution. Smear mounts or grain mounts (slides with individual, disaggregated grains smeared or settled out onto the slide surface) are an aid in examining small grains where the material can be disaggregated into individual components. In most cases however, scanning and transmission electron microscopy are proved to be the most effective techniques for the detailed examination of fine-grained sediments.

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