Tuff in the context of Tuffite

The Alban Hills (Italian: Colli Albani) are the caldera remains of a quiescent volcanic complex in Italy, located 20 km (12 mi) southeast of Rome and about 24 km (15 mi) north of Anzio. The 950 m (3,120 ft) high Monte Cavo forms a highly visible peak in the centre of the caldera, but the highest point is Maschio delle Faete approximately 2 km (1.2 mi) to the east of Cavo and 6 m (20 ft) taller. There are subsidiary calderas along the rim of the Alban Hills that contain the lakes Albano and Nemi. The hills are composed of peperino (lapis albanus), a variety of tuff that is useful for construction and provides a mineral-rich substrate for nearby vineyards.

The Colosseum (/ˌkɒləˈsiːəm/ KOL-ə-SEE-əm; Italian: Colosseo [kolosˈsɛːo], ultimately from Ancient Greek word "kolossos" meaning a large statue or giant) is an elliptical amphitheatre in the centre of the city of Rome, Italy, just east of the Roman Forum. It is the largest ancient amphitheatre ever built, and is the largest standing amphitheatre in the world. Construction began under the Emperor Vespasian (r. 69–79 AD) in 72 and was completed in AD 80 under his successor and heir, Titus (r. 79–81). Further modifications were made during the reign of Domitian (r. 81–96). The three emperors who were patrons of the work are known as the Flavian dynasty, and the amphitheatre was named the Flavian Amphitheatre (Latin: Amphitheatrum Flavium; Italian: Anfiteatro Flavio [aɱfiteˈaːtro ˈflaːvjo]) by later classicists and archaeologists for its association with their family name (Flavius).

The Colosseum is built of travertine limestone, tuff (volcanic rock), and brick-faced Roman concrete. It could hold an estimated 50,000 to 80,000 spectators at various points in its history, having an average audience of some 65,000; it was used for gladiatorial contests and public spectacles including animal hunts, executions, re-enactments of famous battles, dramas based on Roman mythology, and briefly mock sea battles. The building ceased to be used for entertainment in the early medieval era. It was later reused for such purposes as housing, workshops, quarters for a religious order, a fortress, a quarry, and a Christian shrine.

Rhyolite (/ˈraɪ.əlaɪt/ RY-ə-lyte) 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 assemblage is predominantly quartz, sanidine, and plagioclase. It is the extrusive equivalent of granite.

Its high silica content makes rhyolitic magma extremely viscous. This favors explosive eruptions over effusive eruptions, so this type of magma is more often erupted as pyroclastic rock than as lava flows. Rhyolitic ash-flow tuffs are among the most voluminous of continental igneous rock formations.

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 remain as tephra unless hot enough to fuse into pyroclastic rock or tuff. When a volcano explodes, it releases a variety of tephra including ash, cinders, and blocks. These layers settle on the land and, over time, sedimentation occurs incorporating these tephra layers into the geologic record.

The Servian Wall (Latin: Murus Servii Tullii; Italian: Mura Serviane) is 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 10 m (33 ft) in height in places, 3.6 m (12 ft) wide at its base, 11 km (6.8 mi) long, and is believed to have had 16 main gates, of which only one or two have survived, and enclosed a total area of 246 hectares (610 acres). In the 3rd century AD it was superseded by the construction of the larger Aurelian Walls as the city of Rome grew beyond the boundary of the Servian Wall.

Orvieto (Italian: [orˈvjɛːto]) is a city and comune in the Province of Terni, southwestern Umbria, Italy, situated on the flat summit of a large butte of volcanic tuff. The city rises dramatically above the almost-vertical faces of tuff cliffs that are completed by defensive walls built of the same stone.

The Siberian Traps (Russian: Сибирские траппы, romanized: Sibirskiye trappy) are a large region of volcanic rock, known as a large igneous province, in Siberia, Russia. Large volumes of basaltic lava covered a large expanse of Siberia in a flood basalt event. The massive eruptive event that formed the traps is one of the largest known volcanic events in the last 500 million years. The eruptions continued for roughly two million years and spanned the Permian–Triassic boundary, or P–T boundary, which occurred around 251.9 million years ago. The Siberian Traps are believed to be the primary cause of the Permian–Triassic extinction event, the most severe extinction event in the geologic record. Subsequent periods of Siberian Traps activity have been linked to smaller biotic crises, including the Smithian-Spathian, Olenekian-Anisian, Middle-Late Anisian, and Anisian-Ladinian extinction events. Today, the area is covered by about 7 million km (3 million sq mi) of basaltic rock, with a volume of around 4 million km (1 million cu mi).

In 79 AD, Mount Vesuvius, a stratovolcano located in the modern-day region of Campania, erupted, causing one of the deadliest eruptions in history. Vesuvius violently ejected a cloud of super-heated tephra and gases to a height of 33 km (21 mi), ejecting molten rock, pulverized pumice and hot ash at 1.5 million tons per second, ultimately releasing 100,000 times the thermal energy of the atomic bombings of Hiroshima and Nagasaki. The event gives its name to the Vesuvian type of volcanic eruption, characterised by columns of hot gases and ash reaching the stratosphere, although the event also included pyroclastic flows associated with Peléan eruptions.

The event destroyed several Roman towns and settlements in the area. Pompeii and Herculaneum, obliterated and buried underneath massive pyroclastic surges and ashfall deposits, are the most famous examples. Archaeological excavations have revealed much of the towns and the lives of the inhabitants, leading to the area becoming Vesuvius National Park and a UNESCO World Heritage Site.

Schist (/ˈʃɪst/ SHIST) is a medium-grained metamorphic rock generally derived from fine-grained sedimentary rock, like shale. It shows pronounced schistosity (named for the rock). 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 or plates. This texture reflects a high content of platy minerals, such as mica, talc, chlorite, or graphite. These are often interleaved with more granular minerals, such as feldspar or quartz.

Schist typically forms during regional metamorphism accompanying the process of mountain building (orogeny) and usually reflects a medium grade of metamorphism. Schist can form from many different kinds of rocks, including sedimentary rocks such as mudstones and igneous rocks such as tuffs. Schist metamorphosed from mudstone is particularly common and is often very rich in mica (a mica schist). Where the type of the original rock (the protolith) is discernible, the schist is usually given a name reflecting its protolith, such as schistose metasandstone. Otherwise, the names of the constituent minerals will be included in the rock name, such as quartz-felspar-biotite schist.

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 dark-colored inclusions, suggestive of peppercorns.

The typical peperino occurs in the Alban Hills and in Soriano nel Cimino, near Rome, and was used by the ancient Romans under the name of lapis albanus as a building stone and for the basins of fountains.

The Pajarito Plateau is a volcanic plateau in north central New Mexico, United States. The plateau, part of the Jemez Mountains, is bounded on the west by the Sierra de los Valles, the range forming the east rim of the Valles Caldera, and on the east by the Puye escarpment, which rises about 300 to 400 feet (90 to 100 m) above the Rio Grande valley about a mile (1.6 km) west of the river. The Rio Grande passes through White Rock Canyon to the southeast, and the Caja del Rio (Cerros del Rio) across the river is sometimes regarded as part of the plateau. The plateau is occupied by several notable entities, including Bandelier National Monument, the town of Los Alamos and its remote suburb White Rock, and Los Alamos National Laboratory. Elevations range from about 5,600 feet (1,700 meters) at the river to about 7,800 feet (2,400 meters) where the plateau merges into the mountain range.

The Pajarito Plateau is primarily composed of Bandelier Tuff, a voluminous deposit of volcanic tuff laid down in an explosive eruption — in this case, a pair of eruptions from the nearby Valles Caldera. The two ignimbrite-forming eruptions occurred about 1.6 million and 1.2 million years ago and ejected about 300 cubic kilometers of rock each. The orange-pink rock formations constituting the resulting ignimbrites are known as the Otowi and Tshirege Members of the Bandelier tuff. The tuff lies on top of a volcanic field, exposed to the east, which used to be continuous with the Caja del Rio (now across the Rio Grande).

Extrusive rock refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff. In contrast, intrusive rock refers to rocks formed by magma which cools below the surface.

The main effect of extrusion is that the magma can cool much more quickly in the open air or under seawater, and there is little time for the growth of crystals. Sometimes, a residual portion of the matrix fails to crystallize at all, instead becoming a natural glass like obsidian.

Ignimbrite is a type of volcanic rock, consisting of a typically welded 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 surrounding atmosphere. New Zealand geologist Patrick Marshall (1869–1950) coined the term ignimbrite from the Latin igni- [fire] and imbri- [rain].

Ignimbrites are made of a very poorly sorted mixture of volcanic ash (or tuff when lithified) and pumice and/or scoria lapilli, commonly with scattered lithic fragments. The ash is composed of glass shards and crystal fragments. Ignimbrites may be fairly loose and unconsolidated, or a poor to strongly lithified (solidified) rock called lapilli tuff. Near the volcanic source, ignimbrites often contain thick accumulations of lithic blocks, and distally, many show meter-thick accumulations of rounded cobbles of pumice. Ignimbrites may be white, grey, pink, beige, brown, or black depending on their composition and density. Many pale ignimbrites are dacitic or rhyolitic. Darker-coloured ignimbrites may be densely welded volcanic glass or, less commonly, mafic in composition.

Metavolcanic rock is volcanic rock that shows signs of having experienced metamorphism. In other words, the rock was originally produced by a volcano, either as lava or tephra. The rock was then subjected to high pressure, high temperature or both, for example by burial under younger rocks, causing the original volcanic rock to recrystallize. Metavolcanic rocks are sometimes described informally as metavolcanics.

When it is possible to determine the original volcanic rock type from the properties of the metavolcanic rock (particularly if the degree of metamorphism is slight), the rock is more precisely named by appylying the prefix meta- to the original rock type. For example, a weakly metamorphosed basalt would be described as a metabasalt, or a weakly metamorphosed tuff as a metatuff.

Bentonite (/ˈbɛntənaɪt/ BEN-tə-nyte) is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-montmorillonite.

Bentonite usually forms from the weathering of volcanic ash in seawater, or by hydrothermal circulation through the porosity of volcanic ash beds, which converts (devitrification) the volcanic glass (obsidian, a volcanic glass with a chemical composition equivalent to rhyolite) present in the ash into clay minerals. In the mineral alteration process, a large fraction (up to 40–50 wt.%) of amorphous silica is dissolved and leached away, leaving the bentonite deposit in place. Bentonite beds are white or pale blue or green (traces of reduced Fe
) in fresh exposures, turning to a cream color and then yellow, red, or brown (traces of oxidized Fe
) as the exposure is weathered further.

A pyroclastic fall deposit is a uniform deposit of material which has been ejected from a volcanic eruption or plume such as an ash fall or tuff. Pyroclastic fallout deposits are a result of:

1. Ballistic transport of ejecta such as volcanic blocks, volcanic bombs and lapilli from volcanic explosions
2. Deposition of material from convective clouds associated with pyroclastic flows such as coignimbrite falls
3. Ejecta carried in gas streaming from a vent. The material under the action of gravity will settle out from an eruption plume or eruption column
4. Ejecta settling from an eruptive plume or eruption column that is displaced laterally by wind currents and is dispersed over great distances