How Shale is Formed

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. These minerals become shale by a process of compaction. As the fine particles that compose shale can remain suspended in water long after all other material has been deposited Shales therefore, 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.

The shales of interest, for shale gas, tend to be Black in colour. The dark colour is the result of the presence of carbon (organic material) and indicates an oxygen free (reducing) sedimentary environment.