IUGS classification of aphanitic extrusive igneous rocks to their relative alkali (Na2O + K2O) and silica (SiO2) weight contents. Blue area is roughly where alkaline rocks plot; yellow area where subalkaline rocks plot. Original source: *Le Maitre, R.W. (ed.); 1989: A classification of igneous rocks and glossary of terms, Blackwell Science, Oxford.A volcanic rock from Italy with a relatively large six-sided phenocryst (diameter about 1 mm) surrounded by a fine-grained groundmass, as seen in thin section under a petrographic microscope
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.[1] In contrast, intrusive rock refers to rocks formed by magma which cools below the surface.[2]
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.[3] Sometimes, a residual portion of the matrix fails to crystallize at all, instead becoming a natural glass like obsidian.
If the magma contains abundant volatile components which are released as free gas, then it may cool with large or small vesicles (bubble-shaped cavities) such as in pumice, scoria, or vesicular basalt. Other examples of extrusive rocks are rhyolite and andesite.
^"Extrusive rock - geology". Retrieved 21 October 2018.
^Jain, Sreepat (2014). Fundamentals of Physical Geology. New Delhi, India: Springer. ISBN 9788132215394.
^Cite error: The named reference :0 was invoked but never defined (see the help page).
Extrusiverock refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as...
consists of extrusiverock, formed above the surface of the crust. Some geologists use the term plutonic rock synonymously with intrusive rock, but other...
Rare porphyritic volcanic rock Boninite – Ultramafic extrusiverock high in both magnesium and silica Carbonatite – Igneous rock with more than 50% carbonate...
Solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization...
Phonolite is an uncommon shallow intrusive or extrusiverock, of intermediate chemical composition between felsic and mafic, with texture ranging from...
volcanic hazards, such as flank collapse.[citation needed] Extrusiverock Intrusive rock Wilkinson, Bruce H; McElroy, Brandon J; Kesler, Stephen E; Peters...
Tephrite is an igneous, volcanic (extrusive) rock, with aphanitic to porphyritic texture. Mineral content is usually abundant feldspathoids (leucite or...
Basanite (/ˈbæs.əˌnaɪt/) is an igneous, volcanic (extrusive) rock with aphanitic to porphyritic texture. It is composed mostly of feldspathoids, pyroxenes...
classifications exist for igneous rock of unusual compositions, such as ultramafic rock or carbonatites. Where possible, extrusive igneous rocks are also classified...
track whose surface is composed of cinders Extrusiverock – Mode of igneous volcanic rock formation Igneous rock Lapilli – Small pyroclast debris thrown...
eutaxitic texture describes the layered or banded texture in some extrusiverock bodies. It is often caused by the compaction and flattening of glass...
greisen and pegmatite. Quartzolite is an extremely rare type of rock. No extrusiverock equivalent of quartzolite is known. The use of the synonym "silexite"...
tufo. Bentonite – Rock type or absorbent swelling clay Brisbane tuff Eutaxitic texture – Layered or banded texture in some extrusiverock bodies Sillar –...
mottled, streaked, or uniform brown, red, green, gray, or black. It is an extrusiverock that is very resistant to erosion. The pitchstone ridge of An Sgùrr...
Boninite is an extrusiverock high in both magnesium and silica, thought to be usually formed in fore-arc environments, typically during the early stages...
Trap rock, also known as either trapp or trap, is any dark-colored, fine-grained, non-granitic intrusive or extrusive igneous rock. Types of trap rock include...
Miocene intrusive rock, generally strongly weathered and easily cleaved, as well as some dikes and purple and gray andesitic extrusiverock bodies. Faulting...
rocks have bimodal size ranges, meaning the rock is composed of two distinct sizes of crystal. In extrusive rocks, the phenocrysts are surrounded by a...
without crystallisation. They may be either plutonic bodies or volcanic extrusive. Again, erosive forces sculpt their current forms. Metamorphic rocks are...
been used in the Nordic countries to describe a metamorphosed, felsic extrusiverock, corresponding to rhyolite, dacite, or rhyodacite according to IUGS...
and often porphyritic texture between that of volcanic rocks, which are extrusive igneous rocks, and plutonic rocks, which form much deeper in the ground...
A quartz latite is a volcanic rock or fine grained extrusiverock composed mostly of alkali feldspar and plagioclase with some quartz. It forms from the...
-əlt/; US: /bəˈsɔːlt, ˈbeɪsɔːlt/) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium...
ages have a margin of error of millions of years. In 1999, the oldest known rock on Earth was dated to 4.031 ±0.003 billion years, and is part of the Acasta...
eruptions in the Matas consists of mostly boninite, which is a type of extrusiverock usually seen in the Izu-Bonin Island Arc. West Mata and the surrounding...
(granite–rhyolite, syenite–trachyte, granodiorite–dacite etc.) however, these extrusive rocks are often eroded so just the plutonic rocks outcrop. Granitoids...
primary igneous rock on the Wrekin is rhyolite; this has a pinkish colour and is usually banded as it is a slow cooling viscous extrusiverock. Intrusions...
References External links dacite An igneous, volcanic rock with a high iron content. It is an extrusiverock of the same general composition as andesite, but...
Parent range Rocky Mountains San Juan Mountains Sneffels Range Topo map USGS Sams Geology Type of rockExtrusiverock Climbing Easiest route class 5.6...
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