<P> Sandstones are medium - grained rocks composed of rounded or angular fragments of sand size, that often but not always have a cement uniting them together . These sand - size particles are often quartz but there are a few common categories and a wide variety of classification schemes that classify sandstones based on composition . Classification schemes vary widely, but most geologists have adopted the Dott scheme, which uses the relative abundance of quartz, feldspar, and lithic framework grains and the abundance of muddy matrix between these larger grains . </P> <P> Rocks that are classified as mudrocks are very fine grained . Silt and clay represent at least 50% of the material that mudrocks are composed of . Classification schemes for mudrocks tend to vary but most are based on the grain size of the major constituents . In mudrocks, these are generally silt, and clay . </P> <P> According to Blatt, Middleton and Murray mudrocks that are composed mainly of silt particles are classified as siltstones . In turn, rocks that possess clay as the majority particle are called claystones . In geology, a mixture of both silt and clay is called mud . Rocks that possess large amounts of both clay and silt are called mudstones . In some cases the term shale is also used to refer to mudrocks and is still widely accepted by most . However, others have used the term shale to further divide mudrocks based on the percentage of clay constituents . The plate - like shape of clay allows its particles to stack up one on top of another creating laminae or beds . The more clay present in a given specimen, the more laminated a rock is . Shale, in this case, is reserved for mudrocks that are laminated, while mudstone refers those that are not . </P> <Ul> <Li> <P> Red mudrock </P> </Li> <Li> <P> Black Shale </P> </Li> </Ul>

The name of a sedimentary rocks that has large rounded clasts in a fine-grained matrix is