Editing Tuff (section)

==Occurrences==
Tuffs have the potential to be deposited wherever explosive volcanism takes place, and so have a wide distribution in location and age.{{sfn|Philpotts|Ague|2009|p=73}}

===High-silica volcanism===
Rhyolite tuffs contain pumiceous, glassy fragments and small scoriae with [[quartz]], [[alkali]] [[feldspar]], [[biotite]], etc. Iceland,<ref>{{cite journal |last1=Jónasson |first1=K. |title=Rhyolite volcanism in the Krafla central volcano, north-east Iceland |journal=Bulletin of Volcanology |date=December 1994 |volume=56 |issue=6–7 |pages=516–528 |doi=10.1007/BF00302832|bibcode=1994BVol...56..516J |s2cid=129012636 }}</ref> Lipari,<ref>{{cite journal |last1=Crisci |first1=G. M. |last2=Rosa |first2=R. |last3=Lanzafame |first3=G. |last4=Mazzuoli |first4=R. |last5=Sheridan |first5=M. F. |last6=Zuffa |first6=G. G. |display-authors=3|title=Monte guardia sequence: a late-pleistocene eruptive cycle on Lipari (Italy) |journal=Bulletin Volcanologique |date=September 1981 |volume=44 |issue=3 |pages=241–255 |doi=10.1007/BF02600562|bibcode=1981BVol...44..241C |s2cid=128627430 }}</ref> Hungary,<ref>{{cite journal |last1=Zelenka |first1=Tibor |last2=Balázs |first2=Endre |last3=Balogh |first3=Kadosa |last4=Kiss |first4=János |title=Buried Neogene volcanic structures in Hungary |journal=Acta Geologica Hungarica |date=December 2004 |volume=47 |issue=2–3 |pages=177–219 |doi=10.1556/ageol.47.2004.2-3.6|url=http://real.mtak.hu/33118/1/zelenka_eltemtett_vulk_2004.pdf }}</ref> the [[Basin and Range Province|Basin and Range]] of the American southwest, and [[New Zealand]]{{sfn|Philpotts|Ague|2009|p=77}} are among the areas where such tuffs are prominent. In the ancient rocks of [[Wales]],<ref>{{cite journal |last1=Howells |first1=M. F. |last2=Reedman |first2=A. J. |last3=Campbell |first3=S. D. G. |title=The submarine eruption and emplacement of the Lower Rhyolitic Tuff Formation (Ordovician), N Wales |journal=Journal of the Geological Society |date=May 1986 |volume=143 |issue=3 |pages=411–423 |doi=10.1144/gsjgs.143.3.0411|bibcode=1986JGSoc.143..411H |s2cid=129147300 }}</ref> [[Charnwood Forest|Charnwood]],<ref>{{cite journal |last1=Carney |first1=John |title=Igneous processes within late Precambrian volcanic centres near Whitwick, northwestern Charnwood Forest |journal=Mercian Geologist |date=2000 |volume=15 |issue=1 |pages=7–28 |url=http://www.emgs.org.uk/files/mercian_vol13on/Mercian%20Geologist%20volume%2015%202000-2003/Mercian%202000%20v15%20p007%20Precambrian%20igneous%20processes%20Charwood,%20Carney.pdf |access-date=1 October 2020 |archive-date=28 September 2022 |archive-url=https://web.archive.org/web/20220928065307/http://www.emgs.org.uk/files/mercian_vol13on/Mercian%20Geologist%20volume%2015%202000-2003/Mercian%202000%20v15%20p007%20Precambrian%20igneous%20processes%20Charwood,%20Carney.pdf |url-status=dead }}</ref> etc., similar tuffs are known, but in all cases, they are greatly changed by silicification (which has filled them with [[opal]], [[chalcedony]], and quartz) and by devitrification.<ref>{{cite journal |last1=McArthur |first1=A. N. |last2=Cas |first2=R. A. F. |last3=Orton |first3=G. J. |title=Distribution and significance of crystalline, perlitic and vesicular textures in the Ordovician Garth Tuff (Wales) |journal=Bulletin of Volcanology |date=30 November 1998 |volume=60 |issue=4 |pages=260–285 |doi=10.1007/s004450050232|bibcode=1998BVol...60..260M |s2cid=128474768 }}</ref> The frequent presence of rounded corroded quartz crystals, such as occur in rhyolitic lavas, helps to demonstrate their real nature.<ref name=EB1911/>

Welded ignimbrites can be highly voluminous, such as the [[Lava Creek Tuff]] erupted from [[Yellowstone Caldera]] in [[Wyoming]] 631,000 years ago. This tuff had an original volume of at least {{convert|1000|km3|cumi|sp=us}}.<ref>{{cite journal |last1=Matthews |first1=Naomi E. |last2=Vazquez |first2=Jorge A. |last3=Calvert |first3=Andrew T. |title=Age of the Lava Creek supereruption and magma chamber assembly at Yellowstone based on 40 Ar/ 39 Ar and U-Pb dating of sanidine and zircon crystals: AGE OF THE LAVA CREEK SUPERERUPTION |journal=Geochemistry, Geophysics, Geosystems |date=August 2015 |volume=16 |issue=8 |pages=2508–2528 |doi=10.1002/2015GC005881|s2cid=131340369 }}</ref> Lava Creek tuff is known to be at least 1000 times as large as the deposits of the [[1980 eruption of Mount St. Helens]], and it had a [[Volcanic Explosivity Index]] (VEI) of 8, greater than any eruption known in the last 10,000 years.<ref>{{cite web |title=What is a supervolcano? What is a supereruption? |url=https://www.usgs.gov/faqs/what-a-supervolcano-what-a-supereruption?qt-news_science_products=0#qt-news_science_products |website=Natural Hazards |publisher=United States Geological Survey |access-date=30 September 2020}}</ref> Ash flow tuffs cover {{convert|7000|km2|sqmi|sp=us}} of the [[North Island]] of [[New Zealand]] and about {{convert|100000|km2|sqmi|sp=us}} of [[Nevada]]. Ash flow tuffs are the only volcanic product with volumes rivaling those of [[flood basalt]]s.{{sfn|Philpotts|Ague|2009|p=77}}

The Tioga Bentonite of the northeastern United States varies in composition from crystal tuff to tuffaceous shale. It was deposited as ash carried by wind that fell out over the sea and settled to the bottom. It is [[Devonian]] in age and likely came from a vent in central [[Virginia]], where the tuff reaches its maximum thickness of about {{convert|40|meters|feet|sp=us}}.<ref>{{cite journal |last1=Dennison |first1=J. M. |last2=Textoris |first2=D. A. |title=Devonian tioga tuff in Northeastern United States |journal=Bulletin Volcanologique |date=March 1970 |volume=34 |issue=1 |pages=289–294 |doi=10.1007/BF02597791|bibcode=1970BVol...34..289D |s2cid=129708915 }}</ref>

===Alkaline volcanism===
Trachyte tuffs contain little or no quartz, but much [[sanidine]] or [[anorthoclase]] and sometimes oligoclase feldspar, with occasional biotite, augite, and hornblende. In weathering, they often change to soft red or yellow [[claystone]]s, rich in [[kaolin]] with secondary quartz.<ref name=EB1911/> Recent trachyte tuffs are found on the [[Rhine]] (at [[Siebengebirge]]),<ref>{{cite book |last1=Lippolt |first1=H. J. |title=Plateau Uplift |chapter=Distribution of Volcanic Activity in Space and Time |date=1983 |pages=112–120 |doi=10.1007/978-3-642-69219-2_15|isbn=978-3-642-69221-5 }}</ref> in [[Ischia]]<ref>{{cite journal |last1=Gillot |first1=P-Y. |last2=Chiesa |first2=S. |last3=Pasquaré |first3=G. |last4=Vezzoli |first4=L. |title=<33,000-yr K–Ar dating of the volcano–tectonic horst of the Isle of Ischia, Gulf of Naples |journal=Nature |date=September 1982 |volume=299 |issue=5880 |pages=242–245 |doi=10.1038/299242a0|bibcode=1982Natur.299..242G |s2cid=4332634 }}</ref> and near [[Naples]].<ref>{{cite journal |last1=Giannetti |first1=Bernardino |last2=De Casa |first2=Giancarlo |title=Stratigraphy, chronology, and sedimentology of ignimbrites from the white trachytic tuff, Roccamonfina Volcano, Italy |journal=Journal of Volcanology and Geothermal Research |date=March 2000 |volume=96 |issue=3–4 |pages=243–295 |doi=10.1016/S0377-0273(99)00144-4|bibcode=2000JVGR...96..243G }}</ref> Trachyte-carbonatite tuffs have been identified in the [[East African Rift]].<ref>{{cite journal |last1=Macdonald |first1=R. |last2=Kjarsgaard |first2=B. A. |last3=Skilling |first3=I. P. |last4=Davies |first4=G. R. |last5=Hamilton |first5=D. L. |last6=Black |first6=S. |title=Liquid immiscibility between trachyte and carbonate in ash flow tuffs from Kenya |journal=Contributions to Mineralogy and Petrology |date=June 1993 |volume=114 |issue=2 |pages=276–287 |doi=10.1007/BF00307762|bibcode=1993CoMP..114..276M |s2cid=128821707 }}</ref> Alkaline crystal tuffs have been reported from [[Rio de Janeiro (state)|Rio de Janeiro]].<ref>{{cite journal |last1=Motoki |first1=Akihisa |last2=Geraldes |first2=Mauro Cesar |last3=Iwanuch |first3=Woldemar |last4=Vargas |first4=Thais |last5=Motoki |first5=Kenji Freire |last6=Balmant |first6=Alex |last7=Ramos |first7=Marina Nascimento |title=The pyroclastic dyke and welded crystal tuff of the Morro dos Gatos alkaline intrusive complex, State of Rio de Janeiro, Brazil |journal=Rem: Revista Escola de Minas |date=March 2012 |volume=65 |issue=1 |pages=35–45 |doi=10.1590/S0370-44672012000100006|doi-access=free }}</ref>

===Intermediate volcanism===
Andesitic tuffs are exceedingly common. They occur along the whole chain of the [[American Cordillera|Cordilleras]]<ref>{{cite journal |last1=Donnelly-Nolan |first1=Julie M. |last2=Nolan |first2=K. Michael |title=Catastrophic flooding and eruption of ash-flow tuff at Medicine Lake volcano, California |journal=Geology |date=1 October 1986 |volume=14 |issue=10 |pages=875–878 |doi=10.1130/0091-7613(1986)14<875:CFAEOA>2.0.CO;2|bibcode=1986Geo....14..875D }}</ref><ref>{{cite journal |last1=Nokleberg |first1=Warren J. |last2=Jones |first2=David L. |last3=Silberling |first3=Norman J. |title=Origin and tectonic evolution of the Maclaren and Wrangellia terranes, eastern Alaska Range, Alaska |journal=GSA Bulletin |date=1 October 1985 |volume=96 |issue=10 |pages=1251–1270 |doi=10.1130/0016-7606(1985)96<1251:OATEOT>2.0.CO;2|bibcode=1985GSAB...96.1251N }}</ref> and [[Andes]],<ref>{{cite journal |last1=Grunder |first1=Anita L. |author-link1=Anita Grunder|title=Low ?18O silicic volcanic rocks at the Calabozos caldera complex, southern Andes: Evidence for upper-crustal contamination |journal=Contributions to Mineralogy and Petrology |date=1987 |volume=95 |issue=1 |pages=71–81 |doi=10.1007/BF00518031|s2cid=128952431 }}</ref> in the [[West Indies]], New Zealand,<ref>{{cite journal |last1=Cronin |first1=Shane J. |last2=Neall |first2=Vincent E. |last3=Palmer |first3=Alan S. |title=Geological history of the north-eastern ring plain of Ruapehu volcano, New Zealand |journal=Quaternary International |date=January 1996 |volume=34-36 |pages=21–28 |doi=10.1016/1040-6182(95)00066-6|bibcode=1996QuInt..34...21C }}</ref> Japan,<ref>{{cite journal |last1=Tatsumi |first1=Yoshiyuki |last2=Ishizaka |first2=Kyoichi |title=Magnesian andesite and basalt from Shodo-Shima Island, southwest Japan, and their bearing on the genesis of calc-alkaline andesites |journal=Lithos |date=April 1982 |volume=15 |issue=2 |pages=161–172 |doi=10.1016/0024-4937(82)90007-X|bibcode=1982Litho..15..161T }}</ref> etc. In the [[Lake District]],<ref>{{cite journal |last1=Oertel |first1=G. |title=Deformation of a Slaty, Lapillar Tuff in the Lake District, England |journal=Geological Society of America Bulletin |date=1970 |volume=81 |issue=4 |page=1173 |doi=10.1130/0016-7606(1970)81[1173:DOASLT]2.0.CO;2|bibcode=1970GSAB...81.1173O }}</ref> North Wales, [[Lorne, Scotland|Lorne]], the [[Pentland Hills]], the [[Cheviots]], and many other districts of [[Great Britain]], ancient rocks of exactly similar nature are abundant. In color, they are red or brown; their scoriae fragments are of all sizes from huge blocks down to minute granular dust. The cavities are filled with many secondary minerals, such as [[calcite]], [[Chlorite group|chlorite]], quartz, [[epidote]], or chalcedony; in microscopic sections, though, the nature of the original lava can nearly always be made out from the shapes and properties of the little crystals which occur in the decomposed glassy base. Even in the smallest details, these ancient tuffs have a complete resemblance to the modern ash beds of [[Cotopaxi]], [[Krakatoa]], and Mont Pelé.<ref name=EB1911/>

===Mafic volcanism===
[[File:Diamond Head Hawaii From Round Top Rd.JPG|thumb|Diamond Head, a tuff cone]]
[[File:Moai Rano raraku.jpg|thumb|upright|Most of the [[moai]]s in [[Easter Island]] are carved out of [[tholeiite]] basalt tuff.]]

Mafic volcanism typically takes the form of [[Hawaiian eruption]]s that are nonexplosive and produce little ash.<ref>{{cite book |last1=Macdonald |first1=Gordon A. |title=Volcanoes in the sea: the geology of Hawaii |date=1983 |publisher=University of Hawaii Press |location=Honolulu |isbn=0-8248-0832-0 |page=9 |edition=2nd}}</ref> However, interaction between basaltic magma and groundwater or sea water results in hydromagmatic explosions that produce abundant ash. These deposit ash cones that subsequently can become cemented into tuff cones. [[Diamond Head, Hawaii]], is an example of a tuff cone, as is the island of [[Ka'ula]]. The glassy basaltic ash produced in such eruptions rapidly alters to [[palagonite]] as part of the process of lithification.{{sfn|Macdonald|1983|pp=17-20}} 

Although conventional mafic volcanism produce little ash, such ash as is formed may accumulate locally as significant deposits. An example is the Pahala ash of [[Hawaii (island)| Hawaii]] island, which locally is as thick as {{convert|15|meters|feet|sp=us}}. These deposits also rapidly alter to palagonite, and eventually weather to [[laterite]].{{sfn|Macdonald|1983|pp=349-353}} 

Basaltic tuffs are also found in [[County Antrim]], [[Isle of Skye|Skye]], [[Isle of Mull|Mull]], and other places, where [[Paleogene]] volcanic rocks are found; in Scotland, [[Derbyshire]], and Ireland among the [[Carboniferous]] strata, and among the still older rocks of the Lake District, the southern uplands of Scotland, and Wales. They are black, dark green, or red in colour; vary greatly in coarseness, some being full of round spongy bombs a foot or more in diameter; and being often submarine, may contain shale, sandstone, grit, and other sedimentary material, and are occasionally fossiliferous. Recent basaltic tuffs are found in [[Iceland]], the [[Faroe Islands]], [[Jan Mayen]], Sicily, the [[Hawaiian Islands]], [[Samoa]], etc. When weathered, they are filled with calcite, chlorite, [[Serpentine group|serpentine]], and especially where the lavas contain [[nepheline]] or [[leucite]], are often rich in [[zeolite]]s, such as [[analcite]], [[prehnite]], [[natrolite]], [[scolecite]], [[chabazite]], [[heulandite]], etc.<ref name=EB1911/>

===Ultramafic volcanism===
Ultramafic tuffs are extremely rare; their characteristic is the abundance of [[olivine]] or serpentine and the scarcity or absence of [[feldspar]] and [[quartz]].<ref>{{cite journal |last1=Milidragovic |first1=D. |last2=Joyce |first2=N.L. |last3=Zagorevski |first3=A. |last4= Chapman |first4=J.B. |year=2015 |title=Petrology of explosive Middle-Upper Triassic ultramafic rocks in the Mess Creek area, northern Stikine terrane |journal=Geological Fieldwork |pages=2016–1 |url=https://www.researchgate.net/publication/291829005 |access-date=27 July 2021}}</ref>

====Kimberlites====
Occurrences of ultramafic tuff include surface deposits of [[kimberlite]] at [[maar]]s in the [[diamond]]-fields of southern Africa and other regions. The principal variety of kimberlite is a dark bluish-green, serpentine-rich breccia (blue-ground) which, when thoroughly oxidized and weathered, becomes a friable brown or yellow mass (the "yellow-ground").<ref name=EB1911/> These breccias were emplaced as gas–solid mixtures and are typically preserved and mined in [[diatreme]]s that form intrusive pipe-like structures. At depth, some kimberlite breccias grade into root zones of dikes made of unfragmented rock. At the surface, ultramafic tuffs may occur in maar deposits. Because kimberlites are the most common igneous source of diamonds, the transitions from maar to diatreme to root-zone dikes have been studied in detail. Diatreme-[[facies]] kimberlite is more properly called an ultramafic breccia rather than a tuff.

====Komatiites====
[[Komatiite]] tuffs are found, for example, in the [[greenstone belts]] of Canada and South Africa.<ref>{{Cite journal|doi = 10.1016/j.precamres.2015.03.004|title = Mode of emplacement of Archean komatiitic tuffs and flows in the Selkirk Bay area, Melville Peninsula, Nunavut, Canada|year = 2015|last1 = Richan|first1 = Lindsay|last2 = Gibson|first2 = Harold L.|last3 = Houlé|first3 = Michel G.|last4 = Lesher|first4 = C. Michael|journal = Precambrian Research|volume = 263|pages = 174–196|bibcode = 2015PreR..263..174R}}</ref><ref>{{Cite journal|doi = 10.25131/sajg.121.0031|title = Volcanological and petrogenetic characteristics of komatiites of the 3.3 Ga Saw Mill Complex, Weltevreden Formation, Barberton Greenstone Belt, South Africa|year = 2018|last1 = Huber|first1 = M.S.|last2 = Byerly|first2 = G.R.|journal = South African Journal of Geology|volume = 121|issue = 4|pages = 463–486| bibcode=2018SAJG..121..463H |s2cid = 56281060| url=https://digitalcommons.lsu.edu/cgi/viewcontent.cgi?article=4846&context=gradschool_theses |url-access = subscription}}</ref>

===Folding and metamorphism===
[[File:Servian Wall-Termini Station.jpg|thumb|upright|Remains of the ancient [[Servian Walls]] in Rome, made of tuff blocks]]
[[File:Petrie Bight Retaining Wall, Queen Street, Brisbane 03.jpg|thumb|right|19th century embankment wall built of [[Brisbane tuff]], [[Brisbane|City of Brisbane]]]]
In course of time, changes other than weathering may overtake tuff deposits. Sometimes, they are involved in folding and become [[Shear (geology)|sheared]] and [[Cleavage (geology)|cleaved]]. Many of the green [[slate]]s of the English [[Geology of the Lake District|Lake District]] are finely cleaved ashes. In [[Charnwood Forest]] also, the tuffs are slaty and cleaved. The green color is due to the large development of chlorite. Among the crystalline [[schist]]s of many regions, green beds or green schists occur, which consist of quartz, hornblende, chlorite or biotite, [[iron oxide]]s, feldspar, etc., and are probably recrystallized or [[Metamorphism|metamorphosed]] tuffs. They often accompany masses of epidiorite and hornblende – schists which are the corresponding lavas and [[Sill (geology)|sill]]s. Some chlorite-schists also are probably altered beds of volcanic tuff. The "Schalsteins" of [[Devon]] and Germany include many cleaved and partly recrystallized ash-beds, some of which still retain their fragmental structure, though their lapilli are flattened and drawn out. Their steam cavities are usually filled with calcite, but sometimes with quartz. The more completely altered forms of these rocks are platy, green chloritic schists; in these, however, structures indicating their original volcanic nature only sparingly occur. These are intermediate stages between cleaved tuffs and crystalline schists.<ref name=EB1911/>