Claystone

A fine grained sedimentary mudrock made up of at least fifty percent clay sized and clay mineral material, placing it within the same broad family as siltstone, mudstone and shale, all of which are classed together as mudrocks, siliciclastic sedimentary rocks with particles smaller than one sixteenth of a millimeter. Mudrocks as a group are dominated by clay minerals along with quartz and feldspar, and may also contain calcite, dolomite, pyrite and organic carbon, and together they make up roughly half of all sedimentary rock in the geologic record, making them the most abundant erosion product on Earth. Claystone is distinguished from mudstone by its higher clay content, since a mudstone is defined as containing a mixture of silt and clay sized particles with at least one third of each, while claystone requires at least fifty percent clay; it is distinguished from shale by its lack of fissility, the tendency to split readily into thin parallel layers. Because their particles are microscopic and highly susceptible to weathering, mudrocks including claystone remain among the least understood sedimentary rocks, and disagreement persists among geologists over the precise boundaries between them.