Hardened sedimentary rock that is composed primarily of angular silt-sized particles (see silt) and that is not laminated or easily split into thin layers. Siltstones, which are hard and durable, occur in thin layers rarely thick enough to be classified as formations. They are intermediate between sandstones and shales but are not as common as either
Sedimentary rock composed of silt-size (0 004-0 06 mm) particles (i e , silt is coarser than clay, but finer than sand and has a slightly gritty feel when rubbed between the fingers or placed between the front teeth and lightly ground)
a fine-grained, layered sedimentary rock composed primarily of grains between 1/256 mm and 1/16 mm in size Siltstones tend to be "flaggy" and contain hard thin layers They feel grittier than shales or mudstones