Shale is a rock that has been formed from the compression of mud over time. Some black shale contains organic compounds that can be converted to oil or natural gas. Other colors of shale are crushed and mixed with water to create clay.
Shale is also used to produce cement, terra cotta pots, bricks and tile roofs. Historically these items were made of clay, but when resources began to deplete, manufacturers turned to shale as an alternative.
Shale is the most common rock that causes landslides. When it comes into contact with water, it becomes slick and muddy. Excavation of shale is usually the trigger of landslides.