Claystone refers to sedimentary rock that contains more than 50% particles with sizes less than 0.0039 mm and large amounts of clay minerals. A rock is called a claystone when its texture is comparatively loose and is called shale or mudstone when its texture is more consolidated. Most claystones form when fine clastic fragments weathered from a parent rock are transported in a suspended state to the sedimentation region and settle. Some claystones are the product of the in situ accumulation or colloidal consolidation of decomposed aluminium silicate minerals. They usually have pure compositions and hence have some industrial value. The main types of claystone include montmorillonitic claystone, illitic claystone, kaolinitic claystone, mudstone and shale.