Shale is a fine-grained, clastic sedimentary rock composed of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable.Blatt, Harvey and Robert J. Tracy, 1996, Petrology: Igneous, Sedimentary and Metamorphic, 2nd ed., Freeman, pp. 281 - 292 ISBN 0-7167-2438-3 Shale is characterized by thin laminae or parallel layering or bedding less than one centimeter in thickness. Historical mining terminology Before the mid… (More on Shales)