Sedimentary rock | |
Composition | |
---|---|
Clay minerals and quartz |
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g., kaolin, Al2Si2O5(OH)4) and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite.[1] Shale is characterized by its tendency to split into thin layers (laminae) less than one centimeter in thickness. This property is called fissility.[1] Shale is the most common sedimentary rock.[2]
The term shale is sometimes applied more broadly, as essentially a synonym for mudrock, rather than in the narrower sense of clay-rich fissile mudrock.[3]