Siltstone

Siltstone is a sedimentary rock which has a composition intermediate in grain size between the coarser sandstones and the finer mudstones and shales. Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) Sandstone is a Sedimentary rock composed mainly of Sand -size Mineral or rock grains. Mudstone (also called mudrock) is a fine grained Sedimentary rock whose original constituents were Clays or Muds Grain size is up Shale (also called mudstone) is a fine-grained Sedimentary rock whose original constituents were Clay minerals or Muds It is characterized by

Description

As its name implies, it is primarily composed (greater than 2/3) of silt sized particles, defined as grains between 3. Silt is Soil or rock derived Granular material of a Grain size between sand and clay 9 and 62. 5 micrometres or 4 to 8 on the Krumbein phi (φ) scale. A micrometre ( American spelling: micrometer; symbol µm) is one millionth of a Metre, or equivalently one thousandth of a Millimetre William Christian Krumbein (1902-1979 was a notable geologist after whom the Krumbein Medal of the International Association for Mathematical Geology (IAMG was named Siltstones differ significantly from sandstones due to their smaller pores and higher propensity for containing a significant clay fraction. Clay is a naturally occurring material composed primarily of fine-grained Minerals which show plasticity through a variable range of Water content, and Although often mistaken as a shale, siltstone lacks the fissility and laminations which are typical of shale. Shale (also called mudstone) is a fine-grained Sedimentary rock whose original constituents were Clay minerals or Muds It is characterized by Fissility refers to the property of Mudstones to split along layers more or less parallel to the plane of bedding thus becoming described as Shales See Siltstones may contain concretions. A concretion is a volume of Sedimentary rock in which a Mineral cement fills the porosity (i Unless the siltstone is fairly shaly, stratification is likely to be obscure and it tends to weather at oblique angles unrelated to bedding.

Holtzclaw siltstone, Louisville, Kentucky

References

• Folk, R. L. , 1965, Petrology of sedimentary rocks PDF version. Austin: Hemphill’s Bookstore. 2nd ed. 1981, ISBN 0-914696-14-9
• Williams, Howel, Francis J. Turner and Charles M. Gilbert, 1954, Petrography, W. H. Freeman