21 - Shale

Hello friends, Welcome to the Rock Repository at the Department of Geology, Shivaji Science College, Nagpur.

I am Shale, a soft, brittle, fine grained, argillaceous, clastic sedimentary rock made up of clay sized particles. I am composed mostly of clay minerals like kaolinite, smectite, illite and some amounts of calcite and quartz. I am the most abundant of sedimentary rocks accounting for roughly 70 percent of sedimentary rocks in the earth’s crust.  I am often found with layers of limestone and sandstone and typically formed in environments where muds, silts and other sediments are deposited by gentle transporting currents and become compacted for example river floodplains, deep ocean floors and basins of shallow seas. I have a laminated structure and I am fissile meaning I can be split into thin layers that are parallel to the bedding surface plane. My color is dependent on my chemical composition. The presence of hematite and limonite imparts a red color to me whereas the presence of calcite gives me a yellowish color. Some black varieties of me are also found. I have many commercially important applications in particular in the ceramics industry. In addition to that I am also the source rock for many of the world's most important oil and natural gas deposits. You may also find many fossils embedded in me. Thank you for visiting.