Ignimbrite is a volcanic pyroclastic rock, often of dacitic or rhyolitic composition. This article is about volcanoes in geology. ... Pyroclastic rocks are formed from lavas which are ejected into the air, as occur in pyroclastic flows or Plinian eruptions. ... Gray, red, black, altered white/tan, flow-banded pumice dacite Dacite is a high-silica igneous, volcanic rock. ... Rhyolite Rhyolite is an igneous, volcanic (extrusive) rock, of felsic composition, with aphanitic to porphyritic texture. ...

"Ignimbrite" means ‘Fiery Rock Dust Cloud’ (from the Latin igni- (fire) and imbri- (rain)), and forms as the result of immense explosions of pyroclastic dust/ash flowing down the sides of volcanic cones or mountains. Latin is an ancient Indo-European language originally spoken in Latium, the region immediately surrounding Rome. ...

The overall colour of this rock type is usually quite light: most dacitic and rhyolitic examples look white, yellow or beige. Some more mafic examples (though less common) are dark grey, brown, or even almost black. Weathering can sometimes alter light coloured ignimbrite to a pale pink as a result of iron oxidation. Gray, red, black, altered white/tan, flow-banded pumice dacite Dacite is a high-silica igneous, volcanic rock. ... Rhyolite Rhyolite is an igneous, volcanic (extrusive) rock, of felsic composition, with aphanitic to porphyritic texture. ... In geology, mafic minerals and rocks are silicate minerals, magmas, and volcanic and intrusive igneous rocks that have relatively high concentrations of the heavier elements. ... Weathering is the process of breaking down rocks, soils and their minerals through direct, or indirect contact with the atmosphere. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ... The most fundamental reactions in chemistry are the redox processes. ...

Petrology

Light microscope image of a welded ignimbrite (welded tuff) as seen in thin section (Long dimension is several mm). The glass shards (mostly brown) are sometimes welded together in the hot deposit and can be deformed by flow and compaction about crystal fragments (clear).

Ignimbrite is primarily composed of a matrix of volcanic ash (tephra) which is composed of shards and fragments of volcanic glass, pumice fragments and crystals . Image File history File linksMetadata Download high-resolution version (600x627, 320 KB) Microscope image of part of a thin section of an ignimbrite (welded tuff) showing shards (mostly brown glass) deformed during flow and compaction about crystal fragments (clear). ... Image File history File linksMetadata Download high-resolution version (600x627, 320 KB) Microscope image of part of a thin section of an ignimbrite (welded tuff) showing shards (mostly brown glass) deformed during flow and compaction about crystal fragments (clear). ... Tephra refers to air-fall material produced by a volcanic eruption regardless of composition or fragment size. ...

Within the ash matrix, often varying amounts of pea to cobble sized rock fragments (xenoliths, cognate inclusions and exotics), previously cooled rock fragments and other debris occur. A xenolith A xenolith (Greek: foreign rock) is a rock fragment which becomes enveloped in a larger rock during the latters development and hardening. ...

The ash may also contain fragmental crystals blown apart by the explosive eruption. These are usually phenocrysts formed within the magma, but may be exotic crystals sourced from the country rock or previously formed volcanic flows known as xenocrysts. Example of phenocrysts in rhomb porphyry from the Oslo rift area in Norway A phenocryst is a relatively large and usually conspicuous crystal formed in the mass of a porphyritic igneous rock. ...

The appearance of an ignimbrite may be reminiscent of a mudstone or a shale if it grades into an ash tuff, and as it grades into an agglomerate, the rock may take on the appearance of a breccia, with a considerable load of angular broken rock fragments. Welded tuff at Golden Gate in Yellowstone National Park Tuff (from the Italian tufo) is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. ... Agglomerate - Wikipedia /**/ @import /skins-1. ... Breccia, derived from the Latin word for broken, is a sedimentary rock composed of angular fragments in a matrix that may be of a similar or a different material. ...

If erupted when hot, in great enough quantities, the heat and pressure of the volcanic pile and the insulating effect of the layers of hot ignimbrite may cause the rock to fuse into a solid, glassy mass. This is known as a welded tuff, the welded components of which are known as fiamme. Fiamme are fragments of hot volcanic ejecta, generally pumice, that have been deformed by compaction in a pyroclastic flow deposit. ...

Mineralogy

The mineralogy of an ignimbrite is controlled primarily by the chemstry of the source magma; ignimbrites generally have a restricted range of phenocryst species within each flow, but may show evidence of xenocrysts and resorbed xenoliths. A xenolith A xenolith (Greek: foreign rock) is a rock fragment which becomes enveloped in a larger rock during the latters development and hardening. ...

The typical range of phenocrysts in ignimbrites are biotite, quartz, sanidine, albite or other feldspar usually of orthoclase composition, occasionally hornblende, rarely pyroxene and in the case of phonolite tuffs, the feldspathoid minerals such as nepheline and leucite. Orthoclase (KAlSi3O8) is an important tectosilicate mineral, which forms igneous rock. ... Amphibole (Hornblende) Hornblende is a complex inosilicate series of minerals. ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... Phonolite is an igneous, volcanic (extrusive) rock, of felsic composition, with aphanitic to porphyritic texture. ... The feldspathoids are a group of tectosilicate minerals which resemble feldspars but have a different structure and much lower silica content. ... A big crystal of Nepheline from Canaã Massif, Brazil Nepheline, also called nephelite (from Greek: nephos, cloud), is a feldspathoid: a silica-undersaturated aluminosilicate, Na3KAl4Si4O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites. ... Leucite or amphigene is a rock-forming mineral composed of potassium and aluminium metasilicate KAl(SiO3)2. ...

Commonly in most felsic ignimbrites the quartz polymorphs coesite and tridymite are usually found within the welded tuffs and agglomerates. In the majority of cases, it appears that these high-temperature polymorphs of quartz occurred post-eruption as part of an autogenic post-eruptive alteration in some metastable form. Thus although tridymite and coesite are common minerals in ignimbrites, they may not be primary magmatic minerals. Coesite is a form of silicon dioxide that is formed when very high pressure (2–3 gigapascals) and moderately high temperature (700 °C) are applied to quartz. ... Tridymite Tridymite is a high-temperature polymorph of quartz and usually occurs as minute tabular white or colorless pseudo-hexagonal triclinic crystals, or scales, in cavities in acidic volcanic rocks. ... Welded tuff at Golden Gate in Yellowstone National Park Tuff (from the Italian tufo) is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. ... Agglomerate - Wikipedia /**/ @import /skins-1. ... Quartz is one of the most common minerals in the Earths continental crust. ...

Geochemistry

Most pyroclastic rocks and by association ignimbrites are highly felsic, with generally over 65% SiO₂. The chemistry of the ignimbrites, like all elsic rocks, and the resultant mineralogy of phenocryst populations within them, is related mostly to the varying contents of sodium, potassium, calcium, the lesser amounts of iron and magnesium. Felsic is a term used in geology to refer to silicate minerals, magmas, and rocks which are enriched in the lighter elements such as silica, oxygen, aluminium, sodium, and potassium. ...

Some rare ignimbrites may be formed from volatile saturated basalt, where the ignimbrite would ave the geochemistry of a normal basalt. Likewise, kimberlite, lamproite and other rarer alkaline rocks may form ignimbrite deposits and would show the goechemical trends common to their source volcanic rock. Basalt Columnar basalt at Sheepeater Cliff in Yellowstone Basalt (IPA: ) is a common gray to black volcanic rock. ... Hewn kimberlite core sample from the James Bay Lowlands region of Northern Ontario, Canada. ... Lamproite is a peralkaline volcanic rock. ...

Alteration

Large piles of semi-molten ignimbrites tend to create some form of hydrthermal activity as they tend to blanket the wet soil and bury watercourses and rivers. The water from such substrates will exist the ignimbrite blanket in fumaroles, geysers and the like, a process which may take several years, for example after the Novarupta tuff eruption. In the process of boiling off this water, the ignimbrite layer may become altered. This tends to form chimneys and pockets of kaolin-altered rock. Loess field in Germany For the Alternative Metal band, see SOiL. Soil, comprising the pedosphere, is positioned at the interface of the lithosphere with the atmosphere, and hydrosphere. ... Sulfur deposits near a fumarole A fumarole (Latin fumus, smoke) is an opening in Earths (or any other astronomical bodys) crust, often in the neighborhood of volcanoes, which emit steam and gases such as carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrogen sulfide. ... Strokkur geyser, Iceland A geyser is a type of hot spring that erupts periodically, ejecting a column of hot water and steam into the air. ... Novarupta, meaning new eruption, is a volcano located on the Alaska Peninsula in the Katmai area, about 290 miles southwest of Anchorage. ... Metasomatism is a geologic process where metamorphism causes an alteration in a mineral or rock mass that involves a chemical change of the substance with the addition of material, as when chrysolite (olivine) is converted to serpentine basically by the addition of water. ... Kaolin Kaolinite (Aluminium Silicate Hydroxide) Kaolinite is a mineral with the chemical composition Al2Si2O5(OH)4. ...

Morphology and occurrence

Ignimbrite originates from violent eruptions of superheated ash, pumice and gas, a pyroclastic flow or cloud, otherwise known as a nuée ardente. Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 1984 Pyroclastic flows are a common and devastating result of some volcanic eruptions. ...

Ignimbrites form sheets that can cover thousands of square kilometres. Some examples create thick, valley-filling deposits, while others form a landscape-mantling veneer that locally thickens in valleys and other palaeotopographic depressions.

Many igimbrites are loose, unconsolidated deposits, but some exhibit welding, giving the ignimbrite the texture of a solid rock mass, hence the terms commonly used to describe these examples: welded tuff and welded ashflow. Welded tuff at Golden Gate in Yellowstone National Park Tuff (from the Italian tufo) is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. ...

Often, but not always, a caldera will form as a result of an ignimbrite eruption because the magma chamber underneath will drain and thus can no longer support the weight of the rock above. Satellite image of Santorini. ... Magma is molten rock located beneath the surface of the Earth (or any other rocky planet), and which often collects in a magma chamber. ...

Ignimbrite deposits can be voluminous - examples with up to hundreds or even thousands of cubic kilometres are known from individual eruptions in the geological past.

Distribution

Ignimbrites occur worldwide associated with many volcanic provinces having high-silica content magma and the resulting explosive eruptions. Magma is molten rock located beneath the surface of the Earth (or any other rocky planet), and which often collects in a magma chamber. ...

Ignimbrite occurs very commonly around the lower Hunter region of the Australian state of New South Wales. The ignimbrite quarried in the Hunter region at locations such as Martins Creek, Brandy Hill, Seaham (Boral) and at the now disused quarry at Raymond Terrace is a volcanic sedimentation rock of Carboniferous age (280-345 million years). It had an extremely violent origin. This material built up to considerable depth and must have taken years to cool down completely. In the process the materials that made up this mixture fused together into a very tough rock of medium density. The Hunter Valley is a region of New South Wales, approximately 160 kilometres north of Sydney, Australia with an approximate population of 700,000 people, most of which live in the Newcastle metropolitan area. ... Capital Sydney Government Const. ... The Carboniferous is a major division of the geologic timescale that extends from the end of the Devonian period, about 359. ...

Ignimbrite also occurs in the Coromandel region of New Zealand, where the striking, orange-brown ignimbrite cliffs form a distinctive feature of the landscape. The Taupo Volcanic Zone in New Zealand is covered in extensive, flat sheets of ignimbrite erupted from caldera volcanoes during the Pleistocene and Holocene. Coromandel is the name of a town and harbour on the Coromandel Peninsula on the east coast of the North Island of New Zealand. ...

Huge deposits of ignimbrite and tuff cap much of the Sierra Madre Occidental in western Mexico. In the western U.S., massive ignimbrite deposits up to several hundred metres thick occur in the Basin and Range Province, largely in Nevada, western Utah, southern Arizona, and north-central and southern New Mexico. The magmatism in the Basin and Range Province included a massive flare-up of ignimbrite which began about 40 million years ago and largely ended 25 million years ago: the magmatism followed the end of the Laramide orogeny, when deformation and magmatism occurred far east of the plate boundary. Additional eruptions of ignimbrite continued in Nevada until roughly 14 million years ago. Individual eruptions were often enormous, sometimes up to thousands of cubic kilometres in volume. This picture shows an aerial view of the Sierra Madre Occidental crossing the territory of Durango, western Mexico The Sierra Madre Occidental is a mountain range in western Mexico and the extreme southwest of the United States, extending 1500 km from southeast Arizona (south and east of Tucson) southeast through... Motto: (Out Of Many, One) (traditional) In God We Trust (1956 to date) Anthem: The Star-Spangled Banner Capital Washington D.C. Largest city New York City None at federal level (English de facto) Government Federal constitutional republic  - President George Walker Bush (R)  - Vice President Dick Cheney (R) Independence from... Basin and Range index map - USGS The Basin and Range Province is a particular type of topography that covers much of the southwestern United States and northwestern Mexico that is typified by elongate north-south trending arid valleys bounded by mountain ranges which also bound adjacent valleys. ... This article does not adequately cite its references or sources. ... Official language(s) English Capital Salt Lake City Largest city Salt Lake City Area  Ranked 13th  - Total 84,876 sq mi (219,887 km²)  - Width 270 miles (435 km)  - Length 350 miles (565 km)  - % water 3. ... Official language(s) English Capital Phoenix Largest city Phoenix Area  Ranked 6th  - Total 113,998 sq mi (295,254 km²)  - Width 310 miles (500 km)  - Length 400 miles (645 km)  - % water 0. ... Capital Santa Fe Largest city Albuquerque Area  Ranked 5th  - Total 121,665 sq mi (315,194 km²)  - Width 342 miles (550 km)  - Length 370 miles (595 km)  - % water 0. ... The Laramide orogeny was a period of mountain building in western North America, which started in the Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. ...

Use

Yucca Mountain Repository, a U.S. Department of Energy terminal storage facility for spent nuclear reactor and other radioactive waste, is in a deposit of ignimbrite and tuff. Yucca Mountain Yucca Mountain is a ridge-line in Nye County, Nevada, composed of volcanic material (mostly tuff) ejected from a now-extinct caldera-forming supervolcano. ...

The layering of ignimbrites is utilized when the stone is worked, as it sometimes splits into convenient slabs, useful for flagstones and in garden edge landscaping.

In the Hunter region of New South Wales ignimbrite serves as an excellent aggregate or 'blue metal' for road surfacing and construction purposes. This article is about the American English usage of pavement as the durable surfacing of roads and walkways. ...

See also

• Bluestone
• Pyroclastic flow
• Lava
• Magma

This article is about the mineral dolerite. ... Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 1984 Pyroclastic flows are a common and devastating result of some volcanic eruptions. ... Look up lava, Aa, pahoehoe in Wiktionary, the free dictionary. ... Magma is molten rock located beneath the surface of the Earth (or any other rocky planet), and which often collects in a magma chamber. ...

References

• The Mid-Tertiary Ignimbrite Flare-Up (Western US)