tuff or banded trachyte (Brocchi) or leucite phonolite lava (Rosenbusch)
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Tuff is a type of rock made of
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer ...
ejected from a
vent Vent or vents may refer to: Science and technology Biology *Vent, the cloaca region of an animal * Vent DNA polymerase, a thermostable DNA polymerase Geology *Hydrothermal vent, a fissure in a planet's surface from which geothermally heated wate ...
during a
volcanic eruption Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are oft ...
. Following ejection and deposition, the ash is
lithified Lithification (from the Ancient Greek word ''lithos'' meaning 'rock' and the Latin-derived suffix ''-ific'') is the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock. Essentially, lithificatio ...
into a solid rock. 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''). Tuff composed of sandy volcanic material can be referred to as volcanic sandstone. Tuff is a relatively soft rock, so it has been used for construction since ancient times. Because it is common in Italy, the Romans used it often for construction. The
Rapa Nui people The Rapa Nui (Rapa Nui: , Spanish: ) are the Polynesian peoples indigenous to Easter Island. The easternmost Polynesian culture, the descendants of the original people of Easter Island make up about 60% of the current Easter Island population a ...
used it to make most of the ''
moai Moai or moʻai ( ; es, moái; rap, moʻai, , statue) are monolithic human figures carved by the Rapa Nui people on Rapa Nui in eastern Polynesia between the years 1250 and 1500. Nearly half are still at Rano Raraku, the main moai quarry, but ...
'' statues on
Easter Island Easter Island ( rap, Rapa Nui; es, Isla de Pascua) is an island and special territory of Chile in the southeastern Pacific Ocean, at the southeasternmost point of the Polynesian Triangle in Oceania. The island is most famous for its ne ...
. Tuff can be classified as either
igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...
or
sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
. It is usually studied in the context of igneous petrology, although it is sometimes described using sedimentological terms. Tuff is often erroneously called tufa in guidebooks and in television programmes.


Volcanic ash

The material that is expelled in a
volcanic eruption Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are oft ...
can be classified into three types: #
Volcanic gas Volcanic gases are gases given off by active (or, at times, by dormant) volcanoes. These include gases trapped in cavities (vesicles) in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating from lava, from volcani ...
es, a mixture made mostly of steam,
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
, and a sulfur compound (either sulfur dioxide, SO2, or hydrogen sulfide, H2S, depending on the temperature) #
Lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...
, the name of
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...
when it emerges and flows over the surface #
Tephra Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, they re ...
, particles of solid material of all shapes and sizes ejected and thrown through the air 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 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 mm in diameter ( sand-sized or smaller) are called volcanic ash. Volcanic ash is further divided into fine ash, with particle sizes smaller than 0.0625 mm in diameter, and coarse ash, with particle sizes between 0.0625 mm and 2 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 mm to 64 mm in diameter) or agglomerate or pyroclastic
breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...
(particles over 64 mm in diameter) rather than tuff. 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 Volcanic glass is the amorphous solid, amorphous (uncrystallized) product of rapidly cooling magma. Like all types of glass, it is a state of matter intermediate between the closely packed, highly ordered array of a crystal and the highly disorde ...
, and tuff formed predominantly from glass shards is described as vitric tuff. 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. 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. The chemical composition of volcanic ash reflects the entire range of volcanic rock chemistry, from high-silica
rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...
ash to low-silica
basaltic Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of a ...
ash, and tuffs are likewise described as rhyolitic, andesitic, basaltic, and so on.


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 An eruption column or eruption plume is a cloud of super-heated Volcanic ash, ash and tephra suspended in volcanic gas, gases emitted during an explosive volcanic eruption. The volcanic materials form a vertical column or Plume (fluid dynamics), ...
. These fall to the surface as ''fallout'' deposits that are characteristically 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 A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of b ...
and surges that characteristically are poorly sorted and pool in low terrain. Surge deposits sometimes show
sedimentary structures Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition. Sediments and sedimentary rocks are characterized by bedding, which occurs when layers of sediment, with different particl ...
typical of high-velocity flow, such as
dunes A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, fl ...
and
antidunes An antidune is a bedform found in fluvial and other channeled environments. Antidunes occur in supercritical flow, meaning that the Froude number is greater than 1.0 or the flow velocity exceeds the wave velocity; this is also known as upper flow ...
. Volcanic ash already deposited on the surface can be transported as mud flows ( lahars) when mingled with water from rainfall or through eruption into a body of water or ice. 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 . If the rock contains scattered, pea-sized fragments or
fiamme Fiamme are lens-shapes, usually millimetres to centimetres in size, seen on surfaces of some volcaniclastic rocks. They can occur in welded pyroclastic fall deposits and in ignimbrites, which are the deposits of pumiceous pyroclastic density cu ...
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 Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surro ...
s. During welding, the glass shards and pumice fragments adhere together (necking at point contacts), deform, and compact together, resulting in a eutaxitic fabric. Welded tuff is commonly rhyolitic in composition, but examples of all compositions are known. 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. Cooler pyroclastic flows are unwelded and the ash sheets deposited by them are relatively unconsolidated. 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 ground water or sea water, which leaches alkali metals and
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
from the glass. New minerals, such as
zeolite Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H+. These p ...
s,
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
s, and calcite, crystallize from the dissolved substances and cement the tuff. 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. File:Volcanic Ash Fall Layers Izu Oshima Japan 1.jpg, Layers of fallout tuff in Japan File:BishopTuff.jpg, Rocks from the
Bishop tuff The Bishop Tuff is a welded tuff that formed 764,800 ± 600 years ago as a rhyolitic pyroclastic flow during the approximately six day eruption that created the Long Valley Caldera. Large outcrops of the tuff are located in Inyo and Mono Countie ...
in
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
, unwelded with
pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...
on left, welded with
fiamme Fiamme are lens-shapes, usually millimetres to centimetres in size, seen on surfaces of some volcaniclastic rocks. They can occur in welded pyroclastic fall deposits and in ignimbrites, which are the deposits of pumiceous pyroclastic density cu ...
on right File:Bandelier Tuff San Diego Canyon.jpg, Bandelier Tuff at San Diego Canyon. The lower Otowi Member is a single massive cooling unit, while the upper Tshirege Member is composed of multiple cooling units.


Occurrences

Tuffs have the potential to be deposited wherever explosive volcanism takes place, and so have a wide distribution in location and age.


High-silica volcanism

Rhyolite tuffs contain pumiceous, glassy fragments and small scoriae with
quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
, alkali
feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) felds ...
, biotite, etc. Iceland, Lipari, Hungary, the Basin and Range of the American southwest, and
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
are among the areas where such tuffs are prominent. In the ancient rocks of
Wales Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...
, Charnwood, etc., similar tuffs are known, but in all cases, they are greatly changed by silicification (which has filled them with
opal Opal is a hydrated amorphous form of silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline form ...
,
chalcedony Chalcedony ( , or ) is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monocli ...
, and quartz) and by devitrification. The frequent presence of rounded corroded quartz crystals, such as occur in rhyolitic lavas, helps to demonstrate their real nature. Welded ignimbrites can be highly voluminous, such as the
Lava Creek Tuff The Lava Creek Tuff is a tuff formation in Wyoming, Montana and Idaho, United States, created during the Lava Creek eruption around 630,000 years ago, which formed the Yellowstone Caldera. The Lava Creek Tuff is distributed in a radial pattern ar ...
erupted from Yellowstone Caldera in
Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to the s ...
631,000 years ago. This tuff had an original volume of at least . Lava Creek tuff is known to be at least 1000 times as large as the deposits of the
1980 eruption of Mount St. Helens On March 27, 1980, a series of volcanic explosions and pyroclastic flows began at Mount St. Helens in Skamania County, Washington, United States. A series of phreatic blasts occurred from the summit and escalated until a major explosive er ...
, and it had a Volcanic Explosivity Index (VEI) of 8, greater than any eruption known in the last 10,000 years. Ash flow tuffs cover of the North Island of
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
and about of
Nevada Nevada ( ; ) is a state in the Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the 7th-most extensive, ...
. Ash flow tuffs are the only volcanic product with volumes rivaling those of
flood basalt A flood basalt (or plateau basalt) is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava. Many flood basalts have been attributed to the onset of a hotspot reac ...
s. 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 Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...
, where the tuff reaches its maximum thickness of about .


Alkaline volcanism

Trachyte tuffs contain little or no quartz, but much
sanidine Sanidine is the high temperature form of potassium feldspar with a general formula K(AlSi3O8). Sanidine is found most typically in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal sys ...
or anorthoclase and sometimes oligoclase feldspar, with occasional biotite, augite, and hornblende. In weathering, they often change to soft red or yellow claystones, rich in
kaolin Kaolinite ( ) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is an important industrial mineral. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral ...
with secondary quartz. Recent trachyte tuffs are found on the
Rhine ), Surselva, Graubünden, Switzerland , source1_coordinates= , source1_elevation = , source2 = Rein Posteriur/Hinterrhein , source2_location = Paradies Glacier, Graubünden, Switzerland , source2_coordinates= , so ...
(at
Siebengebirge The (), occasionally Sieben Mountains or Seven Mountains, are a hill range of the German Central Uplands on the east bank of the Middle Rhine, southeast of Bonn. Description The area, located in the municipalities of Bad Honnef and König ...
), in
Ischia Ischia ( , , ) is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about from Naples. It is the largest of the Phlegrean Islands. Roughly trapezoidal in shape, it measures approximately east to west ...
and near
Naples Naples (; it, Napoli ; nap, Napule ), from grc, Νεάπολις, Neápolis, lit=new city. is the regional capital of Campania and the third-largest city of Italy, after Rome and Milan, with a population of 909,048 within the city's adminis ...
. Trachyte-carbonatite tuffs have been identified in the East African Rift. Alkaline crystal tuffs have been reported from
Rio de Janeiro Rio de Janeiro ( , , ; literally 'River of January'), or simply Rio, is the capital of the state of the same name, Brazil's third-most populous state, and the second-most populous city in Brazil, after São Paulo. Listed by the GaWC as a ...
.


Intermediate volcanism

Andesitic tuffs are exceedingly common. They occur along the whole chain of the Cordilleras and
Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...
, in the
West Indies The West Indies is a subregion of North America, surrounded by the North Atlantic Ocean and the Caribbean Sea that includes 13 independent island countries and 18 dependencies and other territories in three major archipelagos: the Greate ...
, New Zealand, Japan, etc. In the Lake District, North Wales, Lorne, the
Pentland Hills The Pentland Hills are a range of hills southwest of Edinburgh, Scotland. The range is around in length, and runs southwest from Edinburgh towards Biggar and the upper Clydesdale. Etymology The name is first recorded for the farm of Pentla ...
, the
Cheviots The Cheviot Hills (), or sometimes The Cheviots, are a range of uplands straddling the Anglo-Scottish border between Northumberland and the Scottish Borders. The English section is within the Northumberland National Park. The range includes ...
, and many other districts of
Great Britain Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It i ...
, 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, quartz,
epidote Epidote is a calcium aluminium iron sorosilicate mineral. Description Well developed crystals of epidote, Ca2Al2(Fe3+;Al)(SiO4)(Si2O7)O(OH), crystallizing in the monoclinic system, are of frequent occurrence: they are commonly prismatic in hab ...
, 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 Cotopaxi () is an active stratovolcano in the Andes Mountains, located in Latacunga city of Cotopaxi Province, about south of Quito, and northeast of the city of Latacunga, Ecuador. It is the second highest summit in Ecuador, reaching a h ...
,
Krakatoa Krakatoa (), also transcribed (), is a caldera in the Sunda Strait between the islands of Java and Sumatra in the Indonesian province of Lampung. The caldera is part of a volcanic island group ( Krakatoa archipelago) comprising four islands. T ...
, and Mont Pelé.


Mafic volcanism

Mafic volcanism typically takes the form of
Hawaiian eruption A Hawaiian eruption is a type of volcanic eruption where lava flows from the vent in a relatively gentle, low level eruption; it is so named because it is characteristic of Hawaiian volcanoes. Typically they are effusive eruptions, with basalti ...
s that are nonexplosive and produce little ash. 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 Diamond Head is a volcanic tuff cone on the Hawaiian island of Oahu and known to Hawaiians as Lēahi (). The Hawaiian name is most likely derived from ''lae'' (browridge, promontory) plus ''ahi'' (tuna) because the shape of the ridgeline resem ...
, 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 Palagonite is an alteration product from the interaction of water with volcanic glass of chemical composition similar to basalt. Palagonite can also result from the interaction between water and basalt melt. The water flashes to steam on contact w ...
as part of the process of lithification. 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, which locally is as thick as . These deposits also rapidly alter to palagonite, and eventually weather to laterite. Basaltic tuffs are also found in Skye,
Mull Mull may refer to: Places *Isle of Mull, a Scottish island in the Inner Hebrides ** Sound of Mull, between the Isle of Mull and the rest of Scotland * Mount Mull, Antarctica *Mull Hill, Isle of Man * Mull, Arkansas, a place along Arkansas Highway ...
, Antrim, and other places, where Paleogene volcanic rocks are found; in Scotland,
Derbyshire Derbyshire ( ) is a ceremonial county in the East Midlands, England. It includes much of the Peak District National Park, the southern end of the Pennine range of hills and part of the National Forest. It borders Greater Manchester to the nor ...
, 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 Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...
, the
Faroe Islands The Faroe Islands ( ), or simply the Faroes ( fo, Føroyar ; da, Færøerne ), are a North Atlantic island group and an autonomous territory of the Kingdom of Denmark. They are located north-northwest of Scotland, and about halfway bet ...
,
Jan Mayen Jan Mayen () is a Norwegian volcanic island in the Arctic Ocean with no permanent population. It is long (southwest-northeast) and in area, partly covered by glaciers (an area of around the Beerenberg volcano). It has two parts: larger ...
, Sicily, the Hawaiian Islands,
Samoa Samoa, officially the Independent State of Samoa; sm, Sāmoa, and until 1997 known as Western Samoa, is a Polynesian island country consisting of two main islands ( Savai'i and Upolu); two smaller, inhabited islands ( Manono and Apolima); ...
, etc. When weathered, they are filled with calcite, chlorite, serpentine, and especially where the lavas contain
nepheline Nepheline, also called nephelite (), is a rock-forming mineral in the feldspathoid groupa silica-undersaturated aluminosilicate, Na3 K Al4 Si4 O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatite ...
or
leucite Leucite is a rock-forming mineral of the feldspathoid group, silica-undersaturated and composed of potassium and aluminium tectosilicate KAlSi2O6. Crystals have the form of cubic icositetrahedra but, as first observed by Sir David Brewster in ...
, are often rich in
zeolite Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H+. These p ...
s, such as
analcite Analcime (; ) or analcite is a white, gray, or colorless tectosilicate mineral. Analcime consists of hydrated sodium aluminium silicate in cubic crystalline form. Its chemical formula is Na Al Si2 O6· H2O. Minor amounts of potassium and calci ...
,
prehnite Prehnite is an Silicate minerals, inosilicate of calcium and aluminium with the formula: Ca2Al(AlSi3O10)(OH)2. Limited Fe3+ substitutes for aluminium in the structure. Prehnite crystallizes in the orthorhombic crystal system, and most often forms a ...
,
natrolite Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate with the formula . The type locality is Hohentwiel, Hegau, Germany. It was named natrolite by Martin Heinrich Klapro ...
,
scolecite Scolecite is a tectosilicate mineral belonging to the zeolite group; it is a hydrated calcium silicate, Ca Al2 Si3 O10· 3H2O. Only minor amounts of sodium and traces of potassium substitute for calcium. There is an absence of barium, stron ...
,
chabazite Chabazite ()The New Oxford Dictionary of English (1998) - p. 300 "chabazite /'kabəzʌɪt/ noun "A colourless, pink or yellow zeolite mineral, typically occurring as rhombohedral crystals.". is a tectosilicate mineral of the zeolite group, clos ...
,
heulandite Heulandite is the name of a series of tecto-silicate minerals of the zeolite group. Prior to 1997, heulandite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a ser ...
, etc.


Ultramafic volcanism

Ultramafic tuffs are extremely rare; their characteristic is the abundance of
olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
or serpentine and the scarcity or absence of
feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) felds ...
and
quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
.


Kimberlites

Occurrences of ultramafic tuff include surface deposits of
kimberlite Kimberlite is an igneous rock and a rare variant of peridotite. It is most commonly known to be the main host matrix for diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an diamond called the Star of S ...
at maars in the
diamond Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, ...
-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"). These breccias were emplaced as gas–solid mixtures and are typically preserved and mined in
diatreme A diatreme, sometimes known as a maar-diatreme volcano, is a volcanic pipe formed by a gaseous explosion. When magma rises up through a crack in Earth's crust and makes contact with a shallow body of groundwater, rapid expansion of heated wate ...
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 Greenstone belts are zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks that occur within Archaean and Proterozoic cratons between granite and gneiss bodies. The name comes from the green h ...
of Canada and South Africa.


Folding and metamorphism

In course of time, changes other than weathering may overtake tuff deposits. Sometimes, they are involved in folding and become sheared and cleaved. Many of the green slates of the English 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 Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes ...
s of many regions, green beds or green schists occur, which consist of quartz, hornblende, chlorite or biotite, iron oxides, feldspar, etc., and are probably recrystallized or
metamorphosed Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...
tuffs. They often accompany masses of epidiorite and hornblende – schists which are the corresponding lavas and sills. Some chlorite-schists also are probably altered beds of volcanic tuff. The "Schalsteins" of
Devon Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devo ...
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.


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. Tuff is common in Italy, and the
Romans Roman or Romans most often refers to: *Rome, the capital city of Italy * Ancient Rome, Roman civilization from 8th century BC to 5th century AD *Roman people, the people of ancient Rome *''Epistle to the Romans'', shortened to ''Romans'', a lette ...
used it for many buildings and bridges. For example, the whole port of the island of
Ventotene Ventotene (; locally ; la, Pandataria or , from grc, Πανδατερία, Pandatería, or ) is one of the Pontine Islands in the Tyrrhenian Sea, off the coast of Gaeta right at the border between Lazio and Campania, Italy. The municipality ...
(still in use), was carved from tuff. The
Servian Wall The Servian Wall ( la, Murus Servii Tullii; it, Mura Serviane) was an ancient Roman defensive barrier constructed around the city of Rome in the early 4th century BC. The wall was built of volcanic tuff and was up to in height in places, wide ...
, built to defend the city of
Rome , established_title = Founded , established_date = 753 BC , founder = King Romulus (legendary) , image_map = Map of comune of Rome (metropolitan city of Capital Rome, region Lazio, Italy).svg , map_caption ...
in the fourth century BC, is also built almost entirely from tuff. The Romans also cut tuff into small, rectangular stones that they used to create walls in a pattern known as ''
opus reticulatum ''Opus reticulatum'' (also known as reticulate work) is a facing used for concrete walls in Roman architecture from about the first century BCE to the early first century CE. Facings are a type of polygonal masonry used to apply a smooth finish to ...
''. The
peperino Peperino is an Italian word describing a brown or grey volcanic tuff, containing fragments of basalt and limestone, with disseminated crystals of augite, mica, magnetite, leucite, and other similar minerals. The name originally referred to the d ...
, much used at Rome and Naples as a building stone, is a
trachyte Trachyte () is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava enriched with silica and al ...
tuff.
Pozzolana Pozzolana or pozzuolana ( , ), also known as pozzolanic ash ( la, pulvis puteolanus), is a natural siliceous or siliceous- aluminous material which reacts with calcium hydroxide in the presence of water at room temperature (cf. pozzolanic reacti ...
also is a decomposed tuff, but of basic character, originally obtained near
Naples Naples (; it, Napoli ; nap, Napule ), from grc, Νεάπολις, Neápolis, lit=new city. is the regional capital of Campania and the third-largest city of Italy, after Rome and Milan, with a population of 909,048 within the city's adminis ...
and used as a
cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mi ...
, but this name is now applied to a number of substances not always of identical character. In the Eifel region of Germany, a trachytic, pumiceous tuff called
trass Trass is the local name of a volcanic tuff occurring in the Eifel, where it is worked for hydraulic mortar. It is a grey or cream-coloured fragmental rock, largely composed of pumiceous dust, and may be regarded as a trachytic tuff. It much rese ...
has been extensively worked as a hydraulic mortar. Tuff of the Eifel region of
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
has been widely used for construction of railroad stations and other buildings in Frankfurt, Hamburg, and other large cities. Construction using the ''
Rochlitz Rochlitz (; hsb, Rochlica) is a major district town (Große Kreisstadt) in the district of Mittelsachsen, in Saxony, Germany. Rochlitz is the head of the "municipal partnership Rochlitz" (Verwaltungsgemeinschaft Rochlitz) with its other members ...
Porphyr'', can be seen in the
Mannerist Mannerism, which may also be known as Late Renaissance, is a style in European art that emerged in the later years of the Italian High Renaissance around 1520, spreading by about 1530 and lasting until about the end of the 16th century in Ita ...
-style sculpted portal outside the chapel entrance in
Colditz Castle Castle Colditz (or ''Schloss Colditz'' in German) is a Renaissance castle in the town of Colditz near Leipzig, Dresden and Chemnitz in the state of Saxony in Germany. The castle is between the towns of Hartha and Grimma on a hill spur over the r ...
. The trade name ''Rochlitz Porphyr'' is the traditional designation for a dimension stone of
Saxony Saxony (german: Sachsen ; Upper Saxon: ''Saggsn''; hsb, Sakska), officially the Free State of Saxony (german: Freistaat Sachsen, links=no ; Upper Saxon: ''Freischdaad Saggsn''; hsb, Swobodny stat Sakska, links=no), is a landlocked state of ...
with an architectural history over 1,000 years in Germany. The quarries are located near Rochlitz.
Yucca Mountain nuclear waste repository The Yucca Mountain Nuclear Waste Repository, as designated by the Nuclear Waste Policy Act amendments of 1987, is a proposed deep geological repository storage facility within Yucca Mountain for spent nuclear fuel and other high-level radio ...
, 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 The Basin and Range Province is a vast physiographic region covering much of the inland Western United States and northwestern Mexico. It is defined by unique basin and range topography, characterized by abrupt changes in elevation, alternating ...
in
Nevada Nevada ( ; ) is a state in the Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the 7th-most extensive, ...
. In
Napa Valley Napa Valley is an American Viticultural Area (AVA) located in Napa County in California's Wine Country. It was established by the Bureau of Alcohol, Tobacco and Firearms (ATF) on January 27, 1981. Napa Valley is considered one of the premier ...
and
Sonoma Valley Sonoma Valley is a valley located in southeastern Sonoma County, California, in the North Bay region of the San Francisco Bay Area. Known as the birthplace of the California wine industry, the valley is home to some of the earliest vineyards a ...
,
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
, areas made of tuff are routinely excavated for storage of wine barrels. Tuff from Rano Raraku was used by the Rapa Nui people of Easter Island to make the vast majority of their famous
moai Moai or moʻai ( ; es, moái; rap, moʻai, , statue) are monolithic human figures carved by the Rapa Nui people on Rapa Nui in eastern Polynesia between the years 1250 and 1500. Nearly half are still at Rano Raraku, the main moai quarry, but ...
statues. File:Easter-Island.jpg,
Ahu Tongariki Ahu Tongariki () is the largest ahu on Easter Island (Rapa Nui). Its moais were toppled during the island's civil wars, and in the twentieth century the ahu was swept inland by a tsunami. It has since been restored and has fifteen moai, in ...
on Easter Island, with 15
moai Moai or moʻai ( ; es, moái; rap, moʻai, , statue) are monolithic human figures carved by the Rapa Nui people on Rapa Nui in eastern Polynesia between the years 1250 and 1500. Nearly half are still at Rano Raraku, the main moai quarry, but ...
made of tuff from
Rano Raraku Rano Raraku is a volcanic crater formed of consolidated volcanic ash, or tuff, and located on the lower slopes of Terevaka in the Rapa Nui National Park on Easter Island in Chile. It was a quarry for about 500 years until the early eighteenth cent ...
crater: The second moai from the right has a
Pukao Pukao are the hat-like structures or topknots formerly placed on top of some moai statues on Easter Island. They were all carved from a very light-red volcanic scoria, which was quarried from a single source at Puna Pau. Symbolism Pukao were not ...
("topknot") which is made of red
scoria Scoria is a pyroclastic, highly vesicular, dark-colored volcanic rock that was ejected from a volcano as a molten blob and cooled in the air to form discrete grains or clasts.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) '' ...
. Image:20090513090DR Colditz Schloß Portal Kirchenhaus.jpg, The rhyolitic tuff portal of the "church house" at
Colditz Castle Castle Colditz (or ''Schloss Colditz'' in German) is a Renaissance castle in the town of Colditz near Leipzig, Dresden and Chemnitz in the state of Saxony in Germany. The castle is between the towns of Hartha and Grimma on a hill spur over the r ...
,
Saxony Saxony (german: Sachsen ; Upper Saxon: ''Saggsn''; hsb, Sakska), officially the Free State of Saxony (german: Freistaat Sachsen, links=no ; Upper Saxon: ''Freischdaad Saggsn''; hsb, Swobodny stat Sakska, links=no), is a landlocked state of ...
, designed by
Andreas Walther II Andreas ( el, Ἀνδρέας) is a name usually given to males in Austria, Greece, Cyprus, Denmark, Armenia, Estonia, Ethiopia, Eritrea, Finland, Flanders, Germany, Norway, Sweden, Switzerland, Romania, the Netherlands, and Indonesia. The name ...
(1584)


In Armenia

Tuff is used extensively in
Armenia Armenia (), , group=pron officially the Republic of Armenia,, is a landlocked country in the Armenian Highlands of Western Asia.The UNbr>classification of world regions places Armenia in Western Asia; the CIA World Factbook , , and ' ...
and
Armenian architecture Armenian architecture comprises architectural works with an aesthetic or historical connection to the Armenian people. It is difficult to situate this architectural style within precise geographical or chronological limits, but many of its monume ...
. It is the dominant type of stone used in construction in Armenia's capital
Yerevan Yerevan ( , , hy, Երևան , sometimes spelled Erevan) is the capital and largest city of Armenia and one of the world's oldest continuously inhabited cities. Situated along the Hrazdan River, Yerevan is the administrative, cultural, and i ...
,
Gyumri Gyumri ( hy, Գյումրի, ) is an urban municipal community and the second-largest city in Armenia, serving as the administrative center of Shirak Province in the northwestern part of the country. By the end of the 19th century, when the city w ...
, Armenia's second largest city, and
Ani Ani ( hy, Անի; grc-gre, Ἄνιον, ''Ánion''; la, Abnicum; tr, Ani) is a ruined medieval Armenian city now situated in Turkey's province of Kars, next to the closed border with Armenia. Between 961 and 1045, it was the capital of the ...
, the country's medieval capital, now in Turkey. A small village in Armenia was renamed Tufashen (literally "built of tuff") in 1946. File:Yerevan-Republic_Square-12-Government-2019-gje.jpg, Armenia's
Government House Government House is the name of many of the official residences of governors-general, governors and lieutenant-governors in the Commonwealth and the remaining colonies of the British Empire. The name is also used in some other countries. Gover ...
in Yerevan's Republic Square, built of yellow tuff File:Holy_Saviour%27s_Church,_Gyumri.jpg, Holy Saviour's Church in Gyumri, built mainly of black tuff File:Ani-Cathedral, Ruine.jpeg,
Cathedral of Ani The Cathedral of Ani ( hy, Անիի մայր տաճար, ''Anii mayr tačar''; tr, Ani Katedrali) is the largest standing building in Ani, the capital city of medieval Bagratid Armenia, located in present-day eastern Turkey, on the border with ...
, early 11th century, in the medieval Armenian capital of
Ani Ani ( hy, Անի; grc-gre, Ἄνιον, ''Ánion''; la, Abnicum; tr, Ani) is a ruined medieval Armenian city now situated in Turkey's province of Kars, next to the closed border with Armenia. Between 961 and 1045, it was the capital of the ...
(modern-day Turkey) was built in tuff


Tephrochronology

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.Philpotts and Ague 2009, p. 74 Absolute ages for tuff beds can be determined by K-Ar, Ar-Ar, or
carbon-14 dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon. The method was d ...
.
Zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of t ...
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 The Picuris orogeny was an orogenic event in what is now the Southwestern United States from 1.43 to 1.3 billion years ago in the Calymmian Period of the Mesoproterozoic. The event is named for the Picuris Mountains in northern New Mexico and i ...
.


Etymology

The word ''tuff'' is derived from the
Italian Italian(s) may refer to: * Anything of, from, or related to the people of Italy over the centuries ** Italians, an ethnic group or simply a citizen of the Italian Republic or Italian Kingdom ** Italian language, a Romance language *** Regional Ita ...
''tufo''.


See also

* *
Brisbane tuff Brisbane tuff is a type of rock, formed as a result of a volcanic eruption. As the name suggests, it is a type of tuff found in Brisbane, Queensland, Australia. It is a form of welded ignimbrite. Brisbane tuff comes in a variety of colours: p ...
* * *


References


External links

* {{Authority control Tephra Volcanic rocks ko:응회암#용결응회암