The Rock

Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite. When significant amount water is added to shale, it can turn back into clay.
Clay is a naturally occurring material composed primarily of fine-grained minerals.

Shale may be black, gray, red, brown, dark green, or blue. It is fine grained, so particles usually can not be seen. When wet, shale usually smells like wet mud. The rock is made up of clay minerals; Sometimes with some quartz sand, pyrite, gypsum. It was formed when clay sediments settle in quiet lakes, lagoons, bays, or off-shore areas. When buried and compacted the clays become shale. Iron oxides often help to cement the particles together.

How The Clay Got HERE