View source for Tonstein

{{Short description|Type of sedimentary rock}}
[[File:Sandstone-coal-tonsteins (Ericson Sandstone over Rock Springs Formation, Upper Cretaceous; hairpin curve roadcut along Superior Cutoff Road, east of Superior, Wyoming, USA) 15 (48960817658).jpg|thumb|Sandstone-coal tonsteins in Wyoming]]
'''Tonstein''' (from the [[German language|German]] "Ton", meaning clay, plus "Stein", meaning rock) is a hard, compact [[sedimentary rock]] that is composed mainly of [[kaolinite]] or, less commonly, other [[clay mineral]]s such as [[montmorillonite]] and [[illite]]. The clays often are cemented by [[iron oxide]] minerals, [[carbon]]aceous matter, or [[Chlorite group|chlorite]].<ref>{{cite web|url=http://www.chemikus.de/litholexikon/tonstein.htm|title=Tonstein |work=Litholexikon |language=German |publisher=Chemikus-Web }}</ref><ref>{{cite web|url=http://www.geodienst.de/tonstein.htm| title=Tonstein|work=Die Welt der Gesteine |publisher=Geowissenschaftlicher Dienst, Dr. Olaf Otto Dillmann |language=German}}</ref> Tonsteins form from [[volcanic ash]] deposited in swamps.<ref name="PotterOthers2005a"/>
Tonsteins occur as distinctive, thin, and laterally extensive layers in [[coal]] seams throughout the world.  They are often used as [[key bed]]s to correlate the [[strata]] in which they are found. The regional persistence of tonsteins and relict [[phenocryst]]s indicate that they formed as the result of the [[diagenesis|diagenetic alteration]] of [[volcanic ash]] falls in an acidic (low [[pH]]) and low-[[salinity]] environment, consistent with a freshwater [[swamp]].<ref name="PotterOthers2005a">Potter, P. E., J. B. Maynard, and P. J. Depetris (2005) ''Mud and Mudstones'' Springer-Verlag, Heidelberg, Berlin. 297 pp. {{ISBN|3-540-22157-3}}. pp. 141–142.</ref><ref name="BohorOthers1993a">Bohor, B. F., and D. M. Triplehorn (1993) ''Tonsteins: altered volcanic ash layers in coal-bearing sequences'' Special Paper 285. Geological Society of America, Boulder, Colorado, 44 pp. {{ISBN|9780813722856}}</ref> In contrast, the alteration of a volcanic ashfall deposit in a marine environment typically produces a [[bentonite]] layer.<ref name="PotterOthers2005a"/>

The [[indurated|induration]] of tonsteins is in contrast to kaolin [[claystone]]s that can be mined for kaolin clay, such as the [[ball clay]]s found at [[Bovey Tracey]] which formed by the erosion of a nearby kaolinised [[granite]]. These deposits are generally softer, white, and plastic.<ref name="Selley">{{cite book|last=Selley|first=R,C|title=Applied Sedimentology|publisher=[[Elsevier]]| year=2000| edition=2| pages=337| isbn=9780126363753|url=https://books.google.com/books?id=k3PnTbjR0DMC&q=tonstein&pg=PA339|accessdate=28 December 2012}}</ref>

==See also==
* {{annotated link|Claystone}}
* {{annotated link|Lutite}}
* {{annotated link|Mudstone}}
* {{annotated link|Pelite}}
* {{annotated link|Shale}}

==References==
{{reflist}}

==External links==
* R. A. Batchelor, [http://www.st-andrews.ac.uk/~rab/bentrefs.html Bentonite & Tonstein Bibliography], St. Andrews University

[[Category:Sedimentary rocks]]
[[Category:Claystone]]


{{petrology-stub}}