View source for Tuff

{{short description|Rock consolidated from volcanic ash}}
{{Other uses}}
{{distinguish|Tufa}}

{{Infobox rock
|name=Tuff
|type=Igneous
|image= Guadalupe Tuff.jpg
|caption=Tuff from the Guadalupe Formation in [[Luzon]], [[Philippines]]
|composition=[[Volcanic ash]]
|composition_secondary= [[Quartz]], [[feldspars]] ([[sanidine]], [[anorthoclase]], [[plagioclase]]), [[biotite]], [[pyroxene]] ([[augite]]), [[hornblende]], and [[magnetite]]
|class=[[Mafic]] to [[felsic]]
|texture=[[Pyroclastic rock|Pyroclastic]] or [[Eutaxitic texture| Eutaxitic]]}}

[[File:Bandelier-Pockmarked Cliff.jpg|thumb|Cliff face of welded tuff pockmarked with holes — some natural, some man-made — from [[Bandelier National Monument]], [[New Mexico]]]]
[[File:Tufo Necropoli della Banditaccia.JPG|thumb|[[Etruscan architecture|Etruscan]] tuff blocks from a tomb at [[Banditaccia]], Italy]]
[[File:Tuffstein Haus.jpg|thumb|upright|A house constructed of tuff blocks in [[Rieden, Rhineland-Palatinate]], in the [[Volcanic Eifel]] region, Germany]]

'''Tuff''' is a type of [[Rock (geology)|rock]] made of [[volcanic ash]] ejected from a [[Volcano|vent]] during a [[volcanic eruption]]. Following ejection and deposition, the ash [[lithification|lithifies]] into solid rock.<ref>{{cite book |last1=Fisher |first1=Richard V. |last2=Schmincke |first2=H.-U. |title=Pyroclastic rocks |date=1984 |publisher=Springer-Verlag |location=Berlin |isbn=3-540-12756-9 |pages=89–90}}</ref><ref>{{cite book |last1=Schmincke |first1=Hans-Ulrich |title=Volcanism |date=2003 |publisher=Springer |location=Berlin |isbn=978-3-540-43650-8 |page=138}}</ref> Rock that contains greater than 75% ash is considered tuff, while rock containing 25% to 75% ash is described as '''''tuffaceous''''' (for example, ''tuffaceous sandstone'').<ref name="schmidt-1981">{{cite journal |last1=Schmidt |first1=R. |title=Descriptive nomenclature and classification of pyroclastic deposits and fragments: recommendations of the IUGS Subcommission on the Systematics of Igneous Rocks |journal=Geology |volume=9 |year=1981 |issue=2 |pages=41–43 |doi=10.1007/BF01822152 |bibcode=1981GeoRu..70..794S |s2cid=128375559 |url=https://link.springer.com/article/10.1007/BF01822152 |access-date=27 September 2020|url-access=subscription }}</ref> A [[pyroclastic rock]] containing 25–75% [[volcanic bomb]]s or [[volcanic block]]s is called '''tuff breccia'''.<ref>{{cite web|url=https://www.alexstrekeisen.it/english/vulc/pisolitictuff.php|title=Lapillistone|website=Alex Strekeisen|access-date=3 January 2025}}</ref> Tuff composed of sandy volcanic material can be referred to as '''volcanic sandstone'''.<ref>{{cite journal|url=https://journals.lib.unb.ca/index.php/ag/article/view/1257/1648|title=Arenig volcanic and sedimentary strata, central New Brunswick and eastern Maine|year=2003 |doi=10.4138/1257 |access-date=2022-09-24|last1=Poole |first1=W. H. |last2=Neuman |first2=Robert B. |journal=Atlantic Geology |volume=38 |issue=2/3 |doi-access=free }}</ref>

Tuff is a relatively soft rock, so it has been used for construction since ancient times.<ref name="dolan-etal-2019">{{cite journal |last1=Dolan |first1=S.G. |last2=Cates |first2=K.M. |last3=Conrad |first3=C.N. |last4=Copeland |first4=S.R. |title=Home Away from Home: Ancestral Pueblo Fieldhouses in the Northern Rio Grande |journal=Lanl-Ur |date=14 March 2019 |volume=19-21132 |page=96 |url=https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-19-21132 |access-date=29 September 2020}}</ref> Because it is common in Italy, the Romans used it often for construction.<ref name="jackson-etal-2005">{{cite journal |last1=Jackson |first1=M. D. |last2=Marra |first2=F. |last3=Hay |first3=R. L. |last4=Cawood |first4=C. |last5=Winkler |first5=E. M. |display-authors=3|title=The Judicious Selection and Preservation of Tuff and Travertine Building Stone in Ancient Rome* |journal=Archaeometry |date=2005 |volume=47 |issue=3 |pages=485–510 |doi=10.1111/j.1475-4754.2005.00215.x|bibcode=2005Archa..47..485J |doi-access=free }}</ref> The [[Rapa Nui people]] used it to make most of the ''[[moai]]'' statues on [[Easter Island]].<ref name="collins-2016-150-151">{{cite book |last1=Richards |first1=Colin |title=Rapa Nui: Easter Island Cultural and Historical Perspectives |date=2016 |location=Berlin [Germany] |isbn=978-3-7329-0265-1 |pages=160–161 |chapter-url=https://books.google.com/books?id=FPQhDAAAQBAJ&dq=Richards,+Colin.+2016.+%22Making+Moai:+Reconsidering+Concepts+of+Risk+in+the+Construction+of+Megalithic+Architecture+in+Rapa+Nui+(Easter+Island)%22.+Rapa+Nui%E2%80%93Easter+Island:+Cultural+and+Historical+Perspectives,+pp.+150-151&pg=PA149 |access-date=29 July 2021 |chapter=Making Moai: Reconsidering concepts of riskin the construction of megalithic architecture in Rapa Nui (Easter Island)}}</ref>

Tuff can be classified as either [[Igneous rock|igneous]] or [[sedimentary rock]]. It is usually studied in the context of igneous [[petrology]], although it is sometimes described using [[Sedimentology|sedimentological]] terms.

Tuff is often erroneously called [[tufa]] in guidebooks and in television programs, but [[tufa]] is a form of [[travertine]].

==Volcanic ash==
The material that is expelled in a [[Types of volcanic eruptions|volcanic eruption]] can be classified into three types:

# [[Volcanic gas]]es, a mixture made mostly of [[steam]], [[carbon dioxide]], and a sulfur compound (either [[sulfur dioxide]], SO<sub>2</sub>, or [[hydrogen sulfide]], H<sub>2</sub>S, depending on the temperature)
# [[Lava]], the name of [[magma]] when it emerges and flows over the surface
# [[Tephra]], particles of solid material of all shapes and sizes ejected and thrown through the air

[[File:Tuff shards.jpg|thumb|right|Light-microscope image of tuff as seen in thin section (long dimension is several mm): The curved shapes of altered glass shards (ash fragments) are well preserved, although the glass is partly altered. The shapes were formed about bubbles of expanding, water-rich gas.]]

Tephra is made when magma inside the volcano is blown apart by the rapid expansion of hot volcanic gases. Magma commonly explodes as the gas dissolved in it comes out of solution as the pressure decreases [[Extrusive rock|when it flows to the surface]]. These violent explosions produce particles of material that can then fly from the volcano. Solid particles smaller than 2&nbsp;mm in diameter ([[sand|sand-sized]] or smaller) are called volcanic ash.<ref name=EB1911/><ref name="schmidt-1981"/>

Volcanic ash is further divided into fine ash, with particle sizes smaller than 0.0625&nbsp;mm in diameter, and coarse ash, with particle sizes between 0.0625&nbsp;mm and 2&nbsp;mm in diameter. Tuff is correspondingly divided into coarse tuff (coarse ash tuff) and fine tuff (fine ash tuff or dust tuff). Consolidated tephra composed mostly of coarser particles is called lapillistone (particles 2&nbsp;mm to 64&nbsp;mm in diameter) or agglomerate or pyroclastic [[breccia]] (particles over 64&nbsp;mm in diameter) rather than tuff.<ref name="schmidt-1981"/>

Volcanic ash can vary greatly in composition, and so tuffs are further classified by the composition of the ash from which they formed. Ash from high-silica volcanism, particularly in ash flows, consists mainly of shards of [[volcanic glass]],{{sfn|Fisher|Schmincke|1984|p=96}}<ref>{{cite book |last1=Blatt |first1=Harvey |last2=Tracy |first2=Robert J. |title=Petrology: Igneous, Sedimentary, and Metamorphic |date=1996 |publisher=W. H. Freeman |location=New York |isbn=0-7167-2438-3 |pages=27–29 |edition=2nd}}</ref> and tuff formed predominantly from glass shards is described as vitric tuff.<ref name="obrien-1963">{{cite journal |last1=O'Brien |first1=R. T. |title=Classification of tuffs |journal=Journal of Sedimentary Research |date=1 March 1963 |volume=33 |issue=1 |pages=234–235 |doi=10.1306/74D70E20-2B21-11D7-8648000102C1865D|bibcode=1963JSedR..33..234O }}</ref> The glass shards are typically either irregular in shape or are roughly triangular with convex sides. They are the shattered walls of countless small bubbles that formed in the magma as dissolved gases rapidly came out of solution.{{sfn|Blatt|Tracy|1996|pp=27-29}}

Tuffs formed from ash consisting predominantly of individual crystals are described as crystal tuffs, while those formed from ash consisting predominantly of pulverized rock fragments are described as lithic tuffs.<ref name="obrien-1963"/> 

The chemical composition of volcanic ash reflects the entire range of volcanic rock chemistry, from high-silica [[rhyolitic]] ash to low-silica [[basaltic]] ash, and tuffs are likewise described as rhyolitic, andesitic, basaltic, and so on.{{sfn|Fisher|Schmincke|1984|pp=98-99}}

{{anchor|Welded tuff}}

==Transport and lithification==
The most straightforward way for volcanic ash to move away from the vent is as ash clouds that are part of an [[eruption column]]. These fall to the surface as ''fallout'' deposits that are characteristically [[Sorting (geology) |well-sorted]] and tend to form a blanket of uniform thickness across terrain. [[Column collapse]] results in a more spectacular and destructive form of transport, which takes the form of [[pyroclastic flows]] and [[pyroclastic surge|surges]] that characteristically are poorly sorted and pool in low terrain. Surge deposits sometimes show [[sedimentary structures]] typical of high-velocity flow, such as [[dunes]] and [[antidunes]].<ref name="philpotts-ague-2009-77">{{cite book |last1=Philpotts |first1=Anthony R. |last2=Ague |first2=Jay J. |title=Principles of igneous and metamorphic petrology |date=2009 |publisher=Cambridge University Press |location=Cambridge, UK |isbn=978-0-521-88006-0 |page=73 |edition=2nd}}</ref> Volcanic ash already deposited on the surface can be transported as mud flows ([[lahar]]s) when mingled with water from rainfall or through eruption into a body of water or ice.{{sfn|Schmincke|2003|pp=138-157}}

Particles of volcanic ash that are sufficiently hot will weld together after settling to the surface, producing a '''welded tuff'''. Welding requires temperatures in excess of {{convert|600|C|F|sigfig=2|sp=us}}. If the rock contains scattered, pea-sized fragments or [[fiamme]] in it, it is called a welded [[lapilli tuff]]. Welded tuffs (and welded lapilli tuffs) can be of fallout origin, or deposited from ash flows, as in the case of [[ignimbrite]]s.{{sfn|Fisher|Schmincke|1984|p=215}} During welding, the glass shards and pumice fragments adhere together (necking at point contacts), deform, and compact together, resulting in a [[Eutaxitic texture|eutaxitic fabric]].{{sfn|Schmincke|2003|pp=186-187}} Welded tuff is commonly rhyolitic in composition, but examples of all compositions are known.{{sfn|Fisher|Schmincke|1984|p=209}}{{sfn|Blatt|Tracy|1996|p=29}}

A sequence of ash flows may consist of multiple ''cooling units''. These can be distinguished by the degree of welding. The base of a cooling unit is typically unwelded due to chilling from the underlying cold surface, and the degree of welding and of secondary reactions from fluids in the flow increases upwards towards the center of the flow. Welding decreases towards the top of the cooling unit, where the unit cools more rapidly. The intensity of welding may also decrease towards areas in which the deposit is thinner, and with distance from source.<ref>{{cite journal |last1=Ross |first1=Clarence S. |last2=Smith |first2=Robert L. |title=Ash-flow tuffs: Their origin, geologic relations, and identification |journal=USGS Profession Paper Series |series=Professional Paper |date=1961 |issue=366 |doi=10.3133/pp366|doi-access=free |page=19|bibcode=1961usgs.rept....7R |hdl=2027/ucbk.ark:/28722/h26b1t |hdl-access=free }}</ref>

Cooler pyroclastic flows are unwelded and the ash sheets deposited by them are relatively unconsolidated.{{sfn|Schmincke|2003|pp=186-187}} However, cooled volcanic ash can quickly become lithified because it usually has a high content of volcanic glass. This is a thermodynamically unstable material that reacts rapidly with groundwater or seawater, which leaches [[alkali metal]]s and [[calcium]] from the glass. New minerals, such as [[zeolite]]s, [[clay]]s, and [[calcite]], crystallize from the dissolved substances and cement the tuff.{{sfn|Schmincke|2003|p=138}}

Tuffs are further classified by their depositional environment, such as lacustrine tuff, subaerial tuff, or submarine tuff, or by the mechanism by which the ash was transported, such as fallout tuff or ash flow tuff. Reworked tuffs, formed by erosion and redeposition of ash deposits, are usually described by the transport agent, such as aeolian tuff or fluvial tuff.{{sfn|Fisher|Schmincke|1984|pp=89-90}}

<gallery widths="200px" heights="200px">
File:Volcanic Ash Fall Layers Izu Oshima Japan 1.jpg|Layers of fallout tuff in Japan
File:BishopTuff.jpg|Rocks from the [[Bishop tuff]] in [[California]]: unwelded with [[pumice]] on left, welded with [[fiamme]] on right
File:Bandelier Tuff San Diego Canyon.jpg|Bandelier Tuff at San Diego Canyon, New Mexico, US. The lower Otowi Member is a single massive cooling unit, while the upper Tshirege Member is composed of multiple cooling units.
</gallery>

==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 1,000 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 seawater 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 [[Kaʻula]]. 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/>

==Importance==
The primary economic value of tuff is as a building material. In the ancient world, tuff's relative softness meant that it was commonly used for construction where it was available.<ref name="dolan-etal-2019"/> 

===Italy===
Tuff is common in Italy, and the [[Ancient Rome|Romans]] used it for many buildings and bridges.<ref name="jackson-etal-2005"/> For example, the whole port of the island of [[Ventotene]] (still in use), was carved from tuff. The [[Servian Wall]], built to defend the city of [[Rome]] in the fourth century BC, is also built almost entirely from tuff.<ref>{{cite journal |last1=Panei |first1=Liliana |title=The tuffs of the "Servian Wall" in Rome: Materials from the local quarries and from the conquered territories |journal=ArchéoSciences |date=10 April 2010 |issue=34 |pages=39–43 |doi=10.4000/archeosciences.2599|doi-access=free }}</ref> The Romans also cut tuff into small, rectangular stones that they used to create walls in a pattern known as ''[[opus reticulatum]]''.<ref>Giavarini, Carlo, A. Samueli Ferretti, and Maria Laura Santarelli. 2006. [https://books.google.com/books?id=GM47EQvTXeEC&dq=opus+reticulatum&pg=PA107 "Mechanical characteristics of Roman 'opus caementicium'"]. ''Fracture and Failure of Natural Building Stones. Applications in the Restoration of Ancient Monuments.'' pp. 108, 110</ref>

[[Peperino]] has been used in Rome and Naples as a building stone, is a [[trachyte]] tuff. [[Pozzolana]] also is a decomposed tuff, but of basic character, originally obtained near [[Naples]] and used as a [[cement]], but this name is now applied to a number of substances not always of identical character. In the historical architecture of Naples, Neapolitan yellow tuff is the most used building material.<ref>{{cite journal | url=https://doi.org/10.1016/j.conbuildmat.2017.01.053 | doi=10.1016/j.conbuildmat.2017.01.053 | title=The Neapolitan Yellow Tuff: An outstanding example of heterogeneity | date=2017 | last1=Colella | first1=A. | last2=Di Benedetto | first2=C. | last3=Calcaterra | first3=D. | last4=Cappelletti | first4=P. | last5=d'Amore | first5=M. | last6=Di Martire | first6=D. | last7=Graziano | first7=S.F. | last8=Papa | first8=L. | last9=De Gennaro | first9=M. | last10=Langella | first10=A. | journal=Construction and Building Materials | volume=136 | pages=361–373 | bibcode=2017CBMat.136..361C | url-access=subscription }}</ref> [[Piperno]] [[ignimbrite]] tuff was also used widely in Naples and Campania.

===Germany===
In the [[Eifel]] region of Germany, a trachytic, pumiceous tuff called [[trass]] has been extensively worked as a hydraulic [[mortar (masonry)|mortar]].<ref name=EB1911>{{EB1911|wstitle=Tuff|inline=1}}</ref> Tuff of the Eifel region of [[Germany]] has been widely used for construction of railroad stations and other buildings in Frankfurt, Hamburg, and other large cities.{{sfn|Schmincke|2003|pp=280-281}} Construction using the ''[[Rochlitz]] Porphyr'', can be seen in the [[Mannerism|Mannerist]]-style sculpted portal outside the chapel entrance in [[Colditz Castle]].<ref>[[Georg Dehio]]: ''Handbuch der deutschen Kunstdenkmäler, Sachsen II.'' [[Deutscher Kunstverlag]], München, Berlin 1998, p. 160</ref> The trade name ''Rochlitz Porphyr'' is the traditional designation for a [[dimension stone]] of [[Saxony]] with an architectural history over 1,000 years in Germany. The quarries are located near Rochlitz.<ref>Heiner Siedel: ''Sächsische „Porphyrtuffe" aus dem Rotliegend als Baugesteine: Vorkommen und Abbau, Anwendung, Eigenschaften und Verwitterung''. In: Institut für Steinkonservierung e. V. Bericht Nr. 22, 2006, p. 47-58. {{cite web |url=http://www.tu-dresden.de/biw/geotechnik/geologie/publikationen/download/Tuffe_IfS.pdf |title=Archived copy |access-date=2010-05-09  |archive-url=https://web.archive.org/web/20110611074858/http://www.tu-dresden.de/biw/geotechnik/geologie/publikationen/download/Tuffe_IfS.pdf |archive-date=2011-06-11 }}</ref>

===United States===
[[Yucca Mountain nuclear waste repository]], a U.S. Department of Energy terminal storage facility for spent nuclear reactor and other radioactive waste, is in tuff and ignimbrite in the [[Basin and Range Province]] in [[Nevada]].<ref>{{cite journal |last1=Long |first1=Jane C .S. |last2=Ewing |first2=Rodney C. |title=YUCCA MOUNTAIN: Earth-Science Issues at a Geologic Repository for High-Level Nuclear Waste |journal=Annual Review of Earth and Planetary Sciences |date=19 May 2004 |volume=32 |issue=1 |pages=363–401 |doi=10.1146/annurev.earth.32.092203.122444|bibcode=2004AREPS..32..363L }}</ref> In [[Napa Valley]] and [[Sonoma Valley]], [[California]], areas made of tuff are routinely excavated for storage of wine barrels.<ref>{{cite journal |last1=Kositsky |first1=Andrew |last2=Lewis |first2=Scott |title=Seismic Performance of Wine Caves |journal=The World Tunnel Conference |date=2016 |url=https://condorearth.com/wp-content/uploads/2018/02/Seismic-Performance-of-Tunnels-Rev-20160105.pdf |access-date=1 October 2020}}</ref>

===Rapa Nui===
Tuff from Rano Raraku was used by the Rapa Nui people of Easter Island to make the vast majority of their famous [[moai]] statues.<ref name="collins-2016-150-151"/>

<gallery widths="200px" heights="200px">
File:Easter-Island.jpg|[[Ahu Tongariki]] on Easter Island, with 15 [[moai]] made of tuff from [[Rano Raraku]] crater: The second moai from the right has a [[Pukao]] ("topknot") which is made of red [[scoria]].
Image:20090513090DR Colditz Schloß Portal Kirchenhaus.jpg|The rhyolitic tuff portal of the "church house" at [[Colditz Castle]], [[Free State of Saxony|Saxony]], designed by [[Andreas Walther II]] (1584)
</gallery>

===Armenia===
Tuff is used extensively in [[Armenia]] and [[Armenian architecture]].<ref>{{cite book|last=Holding|first=N.|title=Armenia: with Nagorno Karabagh|url=https://books.google.com/books?id=NP8ogKCfrt0C&q=%22volcanic+tuff%22+armenia+building+stone&pg=PA32|access-date=May 26, 2010|year=2006|publisher=[[Bradt Travel Guides]]|isbn=978-1-84162-163-0|page=32}}</ref> It is the dominant type of stone used in construction in Armenia's capital [[Yerevan]],<ref>{{cite news |last1=Billock |first1=Jennifer |title=How Ancient Volcanoes Created Armenia's Pink City |url=https://www.smithsonianmag.com/travel/yerevan-armenias-pink-city-180961506/ |work=[[Smithsonian (magazine)|Smithsonian]] |date=28 December 2016 |archive-url=https://web.archive.org/web/20200609113744/https://www.smithsonianmag.com/travel/yerevan-armenias-pink-city-180961506/ |archive-date=9 June 2020 |quote=...pink tuff is rare outside of the region and Yerevan is the only major city built out of this stone.}}</ref><ref>{{cite news |last1=Lottman |first1=Herbert R. |author-link1=Herbert Lottman |title=Despite Ages of Captivity, The Armenians Persevere |url=https://www.nytimes.com/1976/02/29/archives/despite-ages-of-captivity-the-armenians-persevere-armenia-a-hint-of.html |work=[[The New York Times]] |date=29 February 1976 |quote=The city, whose population is now upwards of 800,000, has been rebuilt in the rosy volcanic stone called tufa...}}</ref> [[Gyumri]], Armenia's second largest city, and [[Ani]], the country's medieval capital, now in Turkey.<ref>{{cite book |last1=Haviland |first1=William A |last2=Harald |first2=E. L. Prins |last3=Dana |first3=Walrath |last4=McBride |first4=Bunny |title=The Essence of Anthropology |date=2015 |publisher=[[Cengage Learning]] |page=[https://books.google.com/books?id=_Th-BAAAQBAJ&dq=ani+tuff+stone&pg=PA137 137] |edition=4th |quote=...walls of monumental buildings at Ani (including the fortifications) were built of smoothly dressed blocks of tuff stone...}}</ref> A small village in Armenia was renamed [[Tufashen]] (literally "built of tuff") in 1946.<ref>{{cite book |last1=Hakobian |first1=T. Kh. |last2=Melik-Bakhshian |first2=St. T. |last3=Barseghian |first3=H. Kh. |author-link1=Tadevos Hakobyan |author-link2=:hy:Ստեփան Մելիք-Բախշյան |author-link3=:hy:Հովհաննես Բարսեղյան |title=Հայաստանի և հարակից շրջանների տեղանունների բառարան [Dictionary of Toponyms of Armenia and Surrounding Regions] Volume V |date=2001 |publisher=Yerevan University Press |page=[http://www.nayiri.com/imagedDictionaryBrowser.jsp?dictionaryId=61&dt=HY_HY&query=%D5%BF%D5%B8%D6%82%D6%86%D5%A1%D5%B7%D5%A5%D5%B6 147] |language=hy |chapter=Տուֆաշեն [Tufashen] }}</ref>

<gallery mode="packed" heights="120" perrow="3">
File:Yerevan-Republic_Square-12-Government-2019-gje.jpg|Armenia's [[Government_House,_Yerevan|Government House]] in Yerevan's [[Republic Square, Yerevan|Republic Square]], built of yellow tuff 
File:Holy_Saviour%27s_Church,_Gyumri.jpg|[[Holy Saviour's Church, Gyumri|Holy Saviour's Church]] in Gyumri, built mainly of black tuff 
File:Ani-Cathedral, Ruine.jpeg|[[Cathedral of Ani]], early 11th century, in the medieval Armenian capital of [[Ani]] (modern-day Turkey) was built in tuff.<ref>{{cite book|last=Hakobyan|first=Tadevos Kh.|author-link=Tadevos Hakobyan|title=Անի մայրաքաղաք [Ani the Capital]|date=1988|publisher=[[Yerevan State University|Yerevan University Press]]|location=Yerevan|page=118|language=hy}}</ref>
</gallery>

===Tephrochronology===
{{Main|Tephrochronology}}
[[File:Pilar Formation outcrop.jpg|thumb|Pilar Formation outcrop showing metatuff beds used for radiometric dating]]

Tuffs are deposited geologically instantaneously and often over a large region. This makes them highly useful as time-stratigraphic markers. The use of tuffs and other tephra deposits in this manner is known as tephrochronology and is particularly useful for [[Quaternary]] chronostratigraphy. Individual tuff beds can be "fingerprinted" by their chemical composition and phenocryst assemblages.<ref name="philpotts-ague-2009-74">Philpotts and Ague 2009, p. 74</ref> Absolute ages for tuff beds can be determined by [[K-Ar]], [[Argon–argon dating|Ar-Ar]], or [[carbon-14 dating]].{{sfn|Fisher|Schmincke|1984|pp=352-356}} [[Zircon]] grains found in many tuffs are highly durable and can survive even metamorphism of the host tuff to schist, allowing absolute ages to be assigned to ancient metamorphic rocks. For example, dating of zircons in a metamorphosed tuff bed in the [[Pilar Formation]] provided some of the first evidence for the [[Picuris orogeny]].<ref>{{cite journal |last1=Daniel |first1=Christopher G. |last2=Pfeifer |first2=Lily S. |last3=Jones |first3=James V III |last4=McFarlane |first4=Christopher M. |title=Detrital zircon evidence for non-Laurentian provenance, Mesoproterozoic (ca. 1490–1450 Ma) deposition and orogenesis in a reconstructed orogenic belt, northern New Mexico, USA: Defining the Picuris orogeny |journal=GSA Bulletin |date=2013 |volume=125 |issue=9–10 |pages=1423–1441 |doi=10.1130/B30804.1 |bibcode=2013GSAB..125.1423D |url=https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/125/9-10/1423/125945/Detrital-zircon-evidence-for-non-Laurentian?redirectedFrom=fulltext |access-date=17 April 2020|url-access=subscription }}</ref>

==Etymology==
The word ''tuff'' is derived from the [[Italian language|Italian]] ''tufo''.<ref>{{cite web | url=https://www.collinsdictionary.com/dictionary/english/tuff | title=Definition of 'tuff' | publisher=HarperCollins | work=Collins English Dictionary | access-date=30 September 2020}}</ref>

==See also==
{{Div col}}
* {{annotated link|Bentonite}}
* [[Brisbane tuff]]
* {{annotated link|Eutaxitic texture}}
* {{annotated link|Sillar}}
* {{annotated link|Tuffite}}
* {{annotated link|Ignimbrite}}, a type of welded tuff
{{Div col end}}

==References==
{{Reflist}}

==External links==
* {{Commonscatinline}}

{{Volcanoes}}
{{Rock type}}
{{Authority control}}

[[Category:Tuff| ]]