changed photo "LvMS-Lvv.jpg" to "Haüyne crystal.JPG" with caption text "A volcanic rock from Italy with a relatively large phenocryst surrounded by a fine-grained groundmass, as seen in thin section under a petrographic microscope"
|
mNo edit summary
|
||
(27 intermediate revisions by 20 users not shown) | |||
Line 1: | Line 1: | ||
|
{{Short description|Mode of igneous volcanic rock formation}} |
||
[[File:Classification extrusive rocks EN.svg|thumb|upright=1.3|[[IUGS]] classification of [[aphanitic]] [[extrusive]] [[igneous rocks]] |
[[File:Classification extrusive rocks EN.svg|thumb|upright=1.3|[[IUGS]] classification of [[aphanitic]] [[extrusive]] [[igneous rocks]] to their relative alkali (Na<sub>2</sub>O + K<sub>2</sub>O) and silica (SiO<sub>2</sub>) weight contents. Blue area is roughly where alkaline rocks plot; yellow area where subalkaline rocks plot. |
||
Original source: |
Original source: |
||
*{{aut|Le Maitre, R.W.}} (''ed.''); '''1989''': ''A classification of igneous rocks and glossary of terms'', Blackwell Science, Oxford. ]] |
*{{aut|Le Maitre, R.W.}} (''ed.''); '''1989''': ''A classification of igneous rocks and glossary of terms'', Blackwell Science, Oxford. ]] |
||
[[File:Haüyne crystal.JPG|thumb|A volcanic rock from Italy with a relatively large phenocryst surrounded by a fine-grained groundmass, as seen in [[thin section]] under a [[petrographic microscope]]]] |
[[File:Haüyne crystal.JPG|thumb|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 [[Earth's atmosphere|atmosphere]] to fall back as [[Pyroclastic rock|pyroclastic]]s or [[tuff]].<ref>{{cite web|url=https://www.britannica.com/science/extrusive-rock|title=Extrusive rock - geology| |
'''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 [[Earth's atmosphere|atmosphere]] to fall back as [[Pyroclastic rock|pyroclastic]]s or [[tuff]].<ref>{{cite web|url=https://www.britannica.com/science/extrusive-rock|title=Extrusive rock - geology|access-date=21 October 2018}}</ref> In contrast, [[intrusive rock]] refers to rocks formed by magma which cools below the surface.<ref name=":3">Jain, Sreepat (2014). ''Fundamentals of Physical Geology''. New Delhi, India: Springer. {{ISBN|9788132215394}}.</ref> |
||
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 [[crystal]]s.<ref name=":0" />Sometimes, a residual portion of the [[matrix (geology)|matrix]] fails to crystallize at all, instead becoming a natural glass |
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 [[crystal]]s.<ref name=":0" /> Sometimes, a residual portion of the [[matrix (geology)|matrix]] fails to [[crystallize]] at all, instead becoming a natural glass like [[obsidian]]. |
||
If the magma contains abundant [[ |
If the magma contains abundant [[Volatile (astrogeology)|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 texture|vesicular]] [[basalt]]. Other examples of extrusive rocks are [[rhyolite]] and [[andesite]]. |
||
⚫ | |||
<br /> |
|||
⚫ | The texture of extrusive rocks is characterized by fine-grained crystals indistinguishable to the human eye, described as [[Aphanite|aphantic]]. Crystals in aphantic rocks are small in size due to their rapid formation during eruption.<ref name=":0">{{Cite book|title=An Introduction to Igneous and Metamorphic Petrology|last=Winter|first=John DuNann|publisher=Prentice-Hall|year=2001|isbn=0132403420|location=Upper Saddle River, New Jersey}}</ref> Any larger crystals visible to the human eye, called [[phenocryst]]s, form earlier while slowly cooling in the magma reservoir.<ref>{{Cite book|title=Volcanism|last=Schmincke|first=Hans-Ulrich|publisher=Springer-Verlag|year=2004|isbn=3540436502|location=New York City, New York}}</ref> When igneous rocks contain two distinct grain sizes, the texture is [[porphyritic]], and the finer crystals are called the [[Matrix (geology)|groundmass]].<ref name=":0" /> The extrusive rocks scoria and pumice have a vesicular, bubble-like, texture due to the presence of vapor bubbles trapped in the magma.<ref name=":1">{{Cite book|title=Practical Volcanology: Lecture Notes for Understanding Volcanic Rocks from Field Based Studies|last=Németh, Károly|first=Martin, Ulrike|publisher=Geological Institute of Hungary|year=2007}}</ref> |
||
⚫ | |||
⚫ | |||
⚫ | [[Shield volcano]]es are large, slow forming volcanoes<ref name=":2">{{Cite book|title=Petrology : Principles and Practice|last=Sen|first=Gautam|publisher=Springer|year=2014|isbn=9783642388002|location=Berlin|oclc=864593152}}</ref> that erupt fluid basaltic magma that cools to form the extrusive rock [[basalt]]. Basalt is composed of minerals readily available in the planet's crust, including [[feldspar]]s and [[pyroxene]]s.<ref name=":3" /> |
||
⚫ |
The texture of extrusive rocks is characterized by fine-grained crystals indistinguishable to the human eye, described as [[Aphanite|aphantic]]. Crystals in aphantic rocks are small in size due to their rapid formation during eruption.<ref name=":0">{{Cite book|title=An Introduction to Igneous and Metamorphic Petrology|last=Winter|first=John DuNann|publisher=Prentice-Hall|year=2001|isbn=0132403420|location=Upper Saddle River, New Jersey |
||
Fissure volcanoes pour out low viscosity basaltic magma from [[fissure vent]]s to form the extrusive rock basalt.<ref name=":3" /> |
|||
⚫ | |||
⚫ |
[[Shield volcano |
||
|
Composite or [[Stratovolcano|stratovolcanoes]] often have andesitic magma and typically form the extrusive rock andesite. Andesitic magma is composed of many gases and melted [[Mantle (geology)|mantle]] rocks.<ref name=":3" /> |
||
[[Cinder cone|Cinder]] or scoria cones violently expel lava with high gas content,<ref name=":3" /> and due to the vapor bubbles in this [[mafic]] lava, the extrusive basalt scoria is formed.<ref name=":2" /> |
|||
Composite or [[Stratovolcano|stratovolcanoes]] often have andesitic magma and typically form the extrusive rock [[andesite]]. Andesitic magma is composed of many gases and melted [[Mantle (geology)|mantle]] rocks.<ref name=":3" /> |
|||
[[ |
[[Lava dome]]s are formed by high viscosity lava that piles up, forming a dome shape. Domes typically solidifytoform the richinsilica extrusive rock [[obsidian]] and sometimes [[dacite]] domes form the extrusive rock dacite, like in the case of [[Mount St. Helens]].<ref name=":3" /> |
||
[[ |
[[Caldera]]s are volcanic depressions formed after an erupted volcano collapses. Resurgent calderas can refill with an eruption of rhyolitic magma to form the extrusive rock rhyolite like the [[Yellowstone Caldera]].<ref name=":3" /> |
||
⚫ | [[Submarine volcano]]es erupt on the ocean floor and produce the extrusive rock pumice.<ref name=":3" /> Pumice is a light-weight glass with a vesicular texture that differs from scoria in its silicic composition and therefore floats.<ref name=":1" /> |
||
[[Caldera|Calderas]] are volcanic depressions formed after an erupted volcano collapses. Resurgent calderas can refill with an eruption of rhyolitic magma to form the extrusive rock [[rhyolite]] like the [[Yellowstone Caldera]].<ref name=":3" /> |
|||
⚫ |
[[Submarine volcano |
||
==See also== |
==See also== |
||
⚫ | |||
* [[Intrusive suite]] |
|||
⚫ | |||
==References== |
==References== |
||
Line 45: | Line 45: | ||
[[Category:Igneous petrology]] |
[[Category:Igneous petrology]] |
||
[[Category: |
[[Category:Igneous rocks]] |
||
{{ |
{{igneous-petrology-stub}} |
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 pyroclasticsortuff.[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.
The texture of extrusive rocks is characterized by fine-grained crystals indistinguishable to the human eye, described as aphantic. Crystals in aphantic rocks are small in size due to their rapid formation during eruption.[3] Any larger crystals visible to the human eye, called phenocrysts, form earlier while slowly cooling in the magma reservoir.[4] When igneous rocks contain two distinct grain sizes, the texture is porphyritic, and the finer crystals are called the groundmass.[3] The extrusive rocks scoria and pumice have a vesicular, bubble-like, texture due to the presence of vapor bubbles trapped in the magma.[5]
Shield volcanoes are large, slow forming volcanoes[6] that erupt fluid basaltic magma that cools to form the extrusive rock basalt. Basalt is composed of minerals readily available in the planet's crust, including feldspars and pyroxenes.[2]
Fissure volcanoes pour out low viscosity basaltic magma from fissure vents to form the extrusive rock basalt.[2]
Composite or stratovolcanoes often have andesitic magma and typically form the extrusive rock andesite. Andesitic magma is composed of many gases and melted mantle rocks.[2]
Cinder or scoria cones violently expel lava with high gas content,[2] and due to the vapor bubbles in this mafic lava, the extrusive basalt scoria is formed.[6]
Lava domes are formed by high viscosity lava that piles up, forming a dome shape. Domes typically solidify to form the rich in silica extrusive rock obsidian and sometimes dacite domes form the extrusive rock dacite, like in the case of Mount St. Helens.[2]
Calderas are volcanic depressions formed after an erupted volcano collapses. Resurgent calderas can refill with an eruption of rhyolitic magma to form the extrusive rock rhyolite like the Yellowstone Caldera.[2]
Submarine volcanoes erupt on the ocean floor and produce the extrusive rock pumice.[2] Pumice is a light-weight glass with a vesicular texture that differs from scoria in its silicic composition and therefore floats.[5]
{{cite book}}
: CS1 maint: multiple names: authors list (link)
Geologic principles and processes
| ||
---|---|---|
Stratigraphic principles |
| |
Petrologic principles |
| |
Geomorphologic processes |
| |
Sediment transport |
| |
![]() | This article about igneous petrology is a stub. You can help Wikipedia by expanding it. |