Shale, sometimes called Mudstone is a fine-grained sedimentary rock made from clay or mud. Shale is the most common type of sedimentary rock, and a large proportion of fossils are found in it.
Shale is often found near water, such as lakes, rivers, lagoons or deltas, and sometimes on continental shelves. They often contain fossils, small impressions of animal tracks, or even what appear to be raindrop patterns, making them of great interest to Geologists eager to find out how they were formed.
Shale can be converted into slate by the application of heat and pressure, which is used in building construction, and for a number of other useful items such as chalk boards.