Siltstone

Siltstone is a clastic sedimentary rock. It is primarily composed (>65%) of silt sized particles, defined as grains 2–62 µm. Siltstones differ significantly from sandstones by their smaller pores and higher propensity for containing a significant clay fraction. Although often mistaken as a shale, siltstone lacks the fissility and laminations which are typical of shale. Siltstones are deposited in calm water environments e.g. near the shores of lakes or deep shelf areas. They commonly occur adjacent to sandstone deposits -- that is, near beaches and delta edges where sand is deposited. The siltstone will grade into shale in deeper water where the suspended clay particles are more abundantly deposited. This example is from the Carboniferous deposits around Huddersfield, Yorkshire. Specimens are provided with a labelled card tray.