Although the petrographic microscope remains the basic tool for analysis of sandstones, petrographic microscopy is being increasingly supplemented by newer analytical methods. Backscattered electron microscopy (BSE) ranks as one of the more useful of these newer techniques because BSE, coupled with energy-dispersive X-ray analysis (EDX), provides a powerful tool for mineral identification, porosity determination, and study of fine-scale grain-to-grain and intragrain relationships (Chapter 3). BSE and EDX can be used, for example, to differentiate easily among such mineral phases as quartz, feldspars, clay minerals, heavy minerals, pyrite, and carbonate and silica cements in sandstones. Mineral identification using BSE and EDX can be particularly advantageous in studying very fine-grained sandstones that are difficult to analyze with a petrographic microscope. Furthermore, techniques exist that allow quantitative mineral identification by automated image analysis techniques – a potential saving in operator time. BSE also allows identification of open pores as small as 0.1 μm; therefore, it is an extremely useful tool for studying porosity and microporosity. Finally, BSE provides a superior method for differentiating within single mineral grains different mineral phases that may have originated through diagenetic processes (e.g., replacement, albitization, dissolution, and precipitation).

QUANTITATIVE IDENTIFICATION OF FRAMEWORK CONSTITUENTS

The fundamental techniques for identifying minerals by using BSE are discussed in Chapters 2 and 9. In these chapters, we describe quantitative techniques for identifying different mineral phases through a combination of X-ray mapping and BSE image analysis, which utilize differences in gray-scale brightness of different mineral phases as displayed in BSE (Tovey and Krinsley, 1991).