Shale Rock

Wednesday, June 16, 2010

Shale is a type of sedimentary rock which was formed from clay that was compacted together by high pressure. Shale is characterized by breaks along thin laminae or parallel layering or bedding less than one centimeter in thickness, called fissility. It exhibits varying degrees of fissility breaking into thin layers, often splintery and usually parallel to the otherwise indistinguishable bedding plane because of parallel orientation of clay mineral flakes. Shale is used to make bricks and other material that is fired in a kiln.

The process in the rock cycle which gives origin to shale is compaction. The fine particles that compose shale can remain suspended in water long after the larger and denser particles of sand have deposited. Shales are typically deposited in very slow moving water and are often found in lakes and lagoonal deposits, in river deltas, on floodplains and offshore from beach sands. They can also be deposited on the continental shelf, in relatively deep, quiet water. Black shales are dark, as a result of being especially rich in unoxidized carbon. Common in some Paleozoic and Mesozoic strata, black shales were deposited in anoxic, reducing environments, such as in stagnant water columns.