Shale
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[[Image:ShaleUSGOV.jpg|thumb|right|Shale]]
'''Shale''' (also called '''mudstone''') is a fine-grained [[sedimentary rock]] whose original constituents were [[clay mineral]]s or [[mud]]s. It is characterized by thin laminae<ref>{{cite encyclopedia
|title = shale
|encyclopedia = Chambers Dictionary of Science and Technology
|publisher = Chambers Harrap Publishers Ltd
|date = 1999}}</ref> breaking with an irregular curving fracture, often splintery and usually parallel to the often-indistinguishable bedding plane. This property is called [[Fissility (geology)|fissility]]. Non-fissile [[Rock (geology)|rocks]] of similar composition but made of particles smaller than 1/16 mm are described as [[mudstone]]s. Rocks with similar particle sizes but with less clay and therefore grittier are [[siltstone]]s. Shale is the most common sedimentary rock.<ref>{{cite web
|url=http://wps.prenhall.com/esm_lutgens_foundations_3/0,6540,354318-,00.html
|title= Rocks: Materials of the Lithosphere - Summary
|publisher=
|accessdate=2007-07-31
}}
</ref>
[[Image:Drill_cuttings_-_Annotated_-_2004.jpg|thumb|right|Sample of [[drill cuttings]] of shale while drilling an [[oil well]] in [[Louisiana]]. Sand grain = 2 mm. in dia.]]
== Formation ==
[[Image:Limestoneshale7342.jpg|thumb|Limey shale overlaid by [[limestone]], [[Cumberland Plateau]], [[Tennessee]]]]
The process in the [[rock cycle]] which forms shale is [[Compaction (geology)|compaction]]. The fine particles that compose shale can remain in water long after the larger and denser particles of sand have deposited. Shales are typically deposited in very slow moving water and are often found in lake and [[lagoon]]al deposits, in [[river delta]]s, on [[floodplain]]s and offshore of beach sands. They can also be deposited on the [[continental shelf]], in relatively deep, quiet water.
'Black shales' are dark, as a result of being especially rich in [[oxidation|unoxidized]] [[carbon]]. Common in some [[Paleozoic]] and [[Mesozoic]] [[stratum|strata]], black shales were deposited in [[anoxia|anoxic]], [[Redox|reducing]] environments, such as in stagnant water columns.
[[Fossil]]s, animal tracks/burrows and even raindrop impact craters are sometimes preserved on shale bedding surfaces. Shales may also contain [[concretion]]s.
Shales that are subject to heat and pressure alter into a hard, fissile, [[metamorphic rock]] known as [[slate]], which is often used in building construction.
[[Image:Shale 8040.jpg|thumb|right|[[Weathering]] shale at a road cut in southeastern [[Kentucky]]]]
==See also==
* [[Bituminous shale]]
* [[Oil shale]]
* [[Burgess shale]]
* [[Barnett Shale]]
* [[Bearpaw Shale]]
* [[Wianamatta shale]]
==Footnotes==
{{reflist}}
==References==
* Blatt, Harvey and Robert J. Tracy, 1996, ''Petrology: Igneous, Sedimentary and Metamorphic'', 2nd ed., Freeman, ISBN 0-7167-2438-3
[[Category:Sedimentary rocks]]
[[ca:Esquist]]
[[cs:Břidlice]]
[[da:Skifer]]
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[[et:Savikilt]]
[[es:Pizarra (roca)]]
[[fr:Schiste]]
[[gl:Xisto]]
[[nl:Schalie]]
[[ja:頁岩]]
[[no:Leirskifer]]
[[fi:Savikivi]]
[[sk:Bridlica (sediment)]]
[[sv:Lerskiffer]]
[[uk:Глинистий сланець]]