Shale Rock: Geology, Composition, Uses ThoughtCo
#0183;#32;Shale is the most common sedimentary rock, accounting for about 70 percent of the rock in the Earth''s crust. Shale is a finegrained rock made from compacted mud and clay. The defining characteristic of shale is its ability to break into layers or fissility. Black and gray shale are common, but the rock can occur in any color.