Mudstone is a fine-grained sedimentary rock. It is usually black or dark grey-brown and is often soft and crumbly.
How is it formed?
Mudstones form when very fine-grained clay particles are deposited in water. They tiny particles settle to the bottom of oceans, lake floors or lagoons or even in quiet stretches of rivers. As the mud is buried and compacted by overlying sediment, the water is squeezed out and it turns into mudstone.