# Tonstein

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{{Short description|Type of sedimentary rock}}
thumb|Sandstone-coal tonsteins in Wyoming
'''Tonstein''' (from the [German](/source/German_language) "Ton", meaning clay, plus "Stein", meaning stone) is a hard, compact [sedimentary rock](/source/sedimentary_rock) that is composed mainly of [kaolinite](/source/kaolinite) or, less commonly, other [clay mineral](/source/clay_mineral)s such as [montmorillonite](/source/montmorillonite) and [illite](/source/illite). The clays often are cemented by [iron oxide](/source/iron_oxide) minerals, [carbon](/source/carbon)aceous matter, or [chlorite](/source/Chlorite_group).<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](/source/volcanic_ash) deposited in swamps.<ref name="PotterOthers2005a"/>
Tonsteins occur as distinctive, thin, and laterally extensive layers in [coal](/source/coal) seams throughout the world.  They are often used as [key bed](/source/key_bed)s to correlate the [strata](/source/strata) in which they are found. The regional persistence of tonsteins and relict [phenocryst](/source/phenocryst)s indicate that they formed as the result of the [diagenetic alteration](/source/diagenesis) of [volcanic ash](/source/volcanic_ash) falls in an acidic (low [pH](/source/pH)) and low-[salinity](/source/salinity) environment, consistent with a freshwater [swamp](/source/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](/source/bentonite) layer.<ref name="PotterOthers2005a"/>

The [induration](/source/indurated) of tonsteins is in contrast to kaolin [claystone](/source/claystone)s that can be mined for kaolin clay, such as the [ball clay](/source/ball_clay)s found at [Bovey Tracey](/source/Bovey_Tracey) which formed by the erosion of a nearby kaolinised [granite](/source/granite). These deposits are generally softer, white, and plastic.<ref name="Selley">{{cite book|last=Selley|first=R,C|title=Applied Sedimentology|publisher=[Elsevier](/source/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}}

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