what is shale

Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. It is characterized by its tendency to split into thin layers less than one centimeter in thickness, a property called fissility. Shale is the most abundant sedimentary rock, accounting for roughly 70 percent of this rock type in the Earth's crust. It is the most common source rock for hydrocarbons, such as natural gas and petroleum, and is used in various industries, including ceramics and cement production