Siltstone

Siltstone is a sedimentary rock that has a grain size in the silt range, finer than sandstone and coarser than claystones.

Siltstone
Sedimentary rock
Siltstone

Description

Siltstone is a clastic sedimentary rock. As its name implies, it is primarily composed (greater than 2/3) of silt sized particles, defined as grains 2–62 μm or 4 to 8 on the Krumbein phi (φ) scale. Siltstones differ significantly from sandstones due to their smaller pores and a higher propensity for containing a significant clay fraction. Although often mistaken for a shale, siltstone lacks the fissility and laminations which are typical of shale. Siltstones may contain concretions. Unless the siltstone is fairly shaly, stratification is likely to be obscure and it tends to weather at oblique angles unrelated to bedding. Mudstone or shale are rocks that contain mud, which is material that has a range of silt and clay. Siltstone is differentiated by having majority silt, not clay.

Holtzclaw siltstone, Louisville, Kentucky

See also
  • Cosmetic palette – made almost exclusively out of siltstone with a few exceptions

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


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