Abstract

Radiographs made from thin slices of rock provide an inexpensive and effective method of obtaining information on the distribution of minerals, fabric, fractures, stratification, and other structural features that may be poorly expressed or invisible in outcrops or hand specimens. The image recorded on the emulsion depends on differences in X-ray absorption by the various constituents of the sample. Thus, variations in composition, texture, cementation, or fabric will outline the internal structure of the rock. Any standard medical or industrial X-ray unit is suitable as an X-ray source. Best results were obtained from specimens approximately 3 mm thick exposed for 2 seconds at 35 K. V. and 30 M. A. from a distance of 1 m. Nonscreen medical film produced the greatest contrast and sharpest detail. Exposure time, type of film, and intensity of radiation may easily be varied to enhance various structures in different rocks. This technique is effective over a wide range of lithology and indicates that many rocks previously described as homogeneous, massive, and structure, less actually contain microcross-strata, horizontal laminae, slump structures, and various other features. It is especially useful in the study of cores where the volume of available rock is small and weathering processes have not accentuated structural detail.

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