View source for Earth:Igneous rock

{{short description|Rock formed through the cooling and solidification of magma or lava}}
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{{World geologic provinces}}

'''Igneous rock''' ({{wikt-lang|en|igneous}} {{etymology|la|{{wikt-lang|la|igneus}}|fiery}}), or '''magmatic rock''', is one of the three main [[Earth:Rock (geology)#Types|rock types]], the others being [[Earth:Sedimentary rock|sedimentary]] and [[Earth:Metamorphic rock|metamorphic]]. Igneous rocks are formed through the cooling and solidification of [[Biology:Magma|magma]] or [[Earth:Lava|lava]].

The magma can be derived from [[Earth:Partial melting|partial melts]] of existing rocks in either a [[Astronomy:Terrestrial planet|planet]]'s [[Earth:Mantle (geology)|mantle]] or [[Earth:Crust (geology)|crust]]. Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in [[Physics:Pressure|pressure]], or a change in composition. Solidification into rock occurs either below the surface as [[Earth:Intrusive rock|intrusive rock]]s or on the surface as extrusive rocks. Igneous rock may form with [[Physics:Crystallization|crystallization]] to form granular, crystalline rocks, or without crystallization to form [[Earth:Volcanic glass|natural glass]]es.

Igneous rocks occur in a wide range of geological settings: shields, platforms, orogens, basins, large igneous provinces, extended crust and oceanic crust.

[[File:Mayon 0021.jpg|thumb|upright=1.35|Volcanic eruptions of lava are major sources of igneous rocks. (Mayon volcano in the Philippines, erupting in 2009)]]

[[File:BasaltColumns PortoSanto.JPG|thumb|upright=1.35|Natural columns of igneous rock separated from each other by columnar joints, in Madeira]]

==Geological significance==
Igneous and metamorphic rocks make up 90–95% of the top {{convert|16|km}} of the Earth's crust by volume.<ref>{{cite book |last1=Prothero |first1=Donald R. |url=https://archive.org/details/sedimentarygeolo0000prot_r6t3/page/12/mode/2up |title=Sedimentary geology : an introduction to sedimentary rocks and stratigraphy |last2=Schwab |first2=Fred |publisher=Freeman |year=2004 |isbn=978-0-7167-3905-0 |edition=2nd |location=New York |page=12 |url-access=registration}}</ref> Igneous rocks form about 15% of the Earth's current land surface.{{refn|group=note|name=first|15% is the arithmetic sum of the area for intrusive plutonic rock (7%) plus the area for extrusive volcanic rock (8%).<ref name="Wilkinson2008">{{cite journal | url=http://gsabulletin.gsapubs.org/content/121/5-6/760.abstract | title=Global geologic maps are tectonic speedometers—Rates of rock cycling from area-age frequencies | first1=Bruce H. | last1=Wilkinson | first2=Brandon J. | last2=McElroy | first3=Stephen E. | last3=Kesler | first4=Shanan E. | last4=Peters | first5=Edward D. | last5=Rothman | journal=Geological Society of America Bulletin | year=2008 | volume=121 | issue=5–6 | pages=760–779 | doi=10.1130/B26457.1 | bibcode=2009GSAB..121..760W}}</ref>}} Most of the Earth's [[Earth:Oceanic crust|oceanic crust]] is made of igneous rock.

Igneous rocks are also geologically important because:
* their minerals and global chemistry give information about the composition of the lower crust or upper mantle from which their parent magma was extracted, and the temperature and pressure conditions that allowed this extraction;<ref>{{cite book |last1=Philpotts |first1=Anthony R. |last2=Ague |first2=Jay J. |title=Principles of igneous and metamorphic petrology |date=2009 |publisher=Cambridge University Press |location=Cambridge, UK |isbn=978-0-521-88006-0 |edition=2nd |pages=356–361}}</ref>
* their [[Physics:Absolute dating|absolute ages]] can be obtained from various forms of [[Physics:Radiometric dating|radiometric dating]] and can be compared to adjacent geological [[Earth:Stratum|strata]], thus permitting calibration of the geological time scale;{{sfn|Philpotts|Ague|2009|p=295}}
* their features are usually characteristic of a specific tectonic environment, allowing tectonic reconstructions (see [[Earth:Plate tectonics|plate tectonics]]);
* in some special circumstances they host important mineral deposits ([[Earth:Ore|ore]]s): for example, [[Chemistry:Tungsten|tungsten]], [[Chemistry:Tin|tin]],<ref>{{cite journal |last1=Heinrich |first1=Christoph A. |title=The chemistry of hydrothermal tin(-tungsten) ore deposition |journal=Economic Geology |date=1 May 1990 |volume=85 |issue=3 |pages=457–481 |doi=10.2113/gsecongeo.85.3.457|bibcode=1990EcGeo..85..457H }}</ref> and [[Chemistry:Uranium|uranium]]<ref>{{cite book |last1=Plant |first1=J.A. |last2=Saunders |first2=A.D. |year=1999 |chapter=Uranium ore deposits |title=Uranium: Mineralogy, geochemistry and the Environment |volume=38 |pages=272–319 |publisher=Walter de Gruyter GmbH & Co KG |isbn=978-1-5015-0919-3 |chapter-url=https://books.google.com/books?id=CbB6DwAAQBAJ&q=uranium+ore+bodies&pg=PA255 |access-date=13 February 2021}}</ref> are commonly associated with [[Chemistry:Granite|granite]]s and [[Earth:Diorite|diorite]]s, whereas ores of [[Chemistry:Chromium|chromium]] and [[Chemistry:Platinum|platinum]] are commonly associated with gabbros.{{sfn|Philpotts|Ague|2009|p=96, 387–388}}

==Geological setting==
[[File:Igneous rock eng modified.jpg|alt=|thumb|Formation of igneous rock]]
Igneous rocks can be either [[Earth:Intrusive rock|intrusive]] (plutonic and hypabyssal) or extrusive ([[Earth:Volcanic rock|volcanic]]).

===Intrusive===
{{main|Earth:Intrusive rock}}
[[File:Intrusion types.svg|thumb|upright=1.3| Basic types of intrusions: {{olist
    |[[Earth:Laccolith|Laccolith]]
    |Small [[Earth:Dike (geology)|dike]]
    |[[Earth:Batholith|Batholith]]
    |Dike
    |[[Earth:Sill (geology)|Sill]]
    |Volcanic neck, pipe
    |[[Earth:Lopolith|Lopolith]]
}}]]

Intrusive igneous rocks make up the majority of igneous rocks and are formed from magma that cools and solidifies within the crust of a planet. Bodies of intrusive rock are known as ''intrusions'' and are surrounded by pre-existing rock (called ''[[Earth:Country rock (geology)|country rock]]''). The country rock is an excellent thermal insulator, so the magma cools slowly, and intrusive rocks are coarse-grained (''phaneritic''). The mineral [[Earth:Crystallite|grain]]s in such rocks can generally be identified with the naked eye. Intrusions can be classified according to the shape and size of the intrusive body and its relation to the bedding of the country rock into which it intrudes. Typical intrusive bodies are [[Earth:Batholith|batholith]]s, stocks, [[Earth:Laccolith|laccolith]]s, [[Earth:Sill (geology)|sill]]s and [[Earth:Dike (geology)|dikes]]. Common intrusive rocks are [[Chemistry:Granite|granite]], gabbro, or [[Earth:Diorite|diorite]].

The central cores of major mountain ranges consist of intrusive igneous rocks. When exposed by erosion, these cores (called ''[[Earth:Batholith|batholith]]s'') may occupy huge areas of the Earth's surface.

Intrusive igneous rocks that form at depth within the crust are termed plutonic (or ''abyssal'') rocks and are usually coarse-grained. Intrusive igneous rocks that form near the surface are termed ''[[Earth:Subvolcanic rock|subvolcanic]]'' or ''hypabyssal'' rocks and they are usually much finer-grained, often resembling volcanic rock.{{sfn|Philpotts|Ague|2009|p=139}} Hypabyssal rocks are less common than plutonic or volcanic rocks and often form dikes, sills, laccoliths, [[Earth:Lopolith|lopolith]]s, or phacoliths.

===Extrusive===
{{main|Earth:Extrusive rock}}
[[File:Volcano q.jpg|thumb|Extrusive igneous rock is made from lava released by volcanoes]]
[[File:Basalt 36mw1041.jpg|thumb|Sample of basalt (an extrusive igneous rock), found in Massachusetts]]
Extrusive igneous rock, also known as volcanic rock, is formed by the cooling of molten magma on the earth's surface. The magma, which is brought to the surface through fissures or volcanic eruptions, rapidly solidifies. Hence such rocks are fine-grained (aphanitic) or even glassy. [[Earth:Basalt|Basalt]] is the most common extrusive igneous rock{{sfn|Philpotts|Ague|2009|pp=52–59}} and forms lava flows, lava sheets and lava plateaus. Some kinds of basalt solidify to form long [[Earth:Columnar jointing|polygonal columns]]. The [[Earth:Giant's Causeway|Giant's Causeway]] in Antrim, Northern Ireland is an example.

The molten rock, which typically contains suspended crystals and dissolved gases, is called [[Biology:Magma|magma]].{{sfn|Philpotts|Ague|2009|pp=19–26}} It rises because it is less dense than the rock from which it was extracted.{{sfn|Philpotts|Ague|2009|pp=28–35}} When magma reaches the surface, it is called [[Earth:Lava|lava]].<ref>{{cite book |last1=Schmincke |first1=Hans-Ulrich |title=Volcanism |date=2003 |publisher=Springer |location=Berlin |isbn=978-3-540-43650-8 |page=295 |doi=10.1007/978-3-642-18952-4|s2cid=220886233 }}</ref> Eruptions of volcanoes into air are termed ''[[Earth:Subaerial|subaerial]]'', whereas those occurring underneath the ocean are termed ''[[Earth:Underwater|submarine]]''. Black smokers and [[Earth:Mid-ocean ridge|mid-ocean ridge]] basalt are examples of submarine volcanic activity.{{sfn|Philpotts|Ague|2009|pp=365–374}}

The volume of extrusive rock erupted annually by volcanoes varies with plate tectonic setting. Extrusive rock is produced in the following proportions:<ref>{{cite book |last1=Fisher |first1=Richard V. |last2=Schmincke |first2=H.-U. |title=Pyroclastic rocks |date=1984 |publisher=Springer-Verlag |location=Berlin |isbn=3-540-12756-9 |page=5}}</ref>
* [[Earth:Divergent boundary|divergent boundary]]: 73%
* [[Earth:Convergent boundary|convergent boundary]] (subduction zone): 15%
* [[Earth:Hotspot (geology)|hotspot]]: 12%.

The behaviour of lava depends upon its [[Physics:Viscosity|viscosity]], which is determined by temperature, composition, and crystal content.  High-temperature magma, most of which is basaltic in composition, behaves in a manner similar to thick oil and, as it cools, [[Chemistry:Treacle|treacle]]. Long, thin basalt flows with pahoehoe surfaces are common. Intermediate composition magma, such as [[Earth:Andesite|andesite]], tends to form cinder cones of intermingled [[Earth:Volcanic ash|ash]], [[Earth:Tuff|tuff]] and lava, and may have a viscosity similar to thick, cold [[Chemistry:Molasses|molasses]] or even rubber when erupted. [[Earth:Felsic|Felsic]] magma, such as [[Earth:Rhyolite|rhyolite]], is usually erupted at low temperature and is up to 10,000 times as viscous as basalt. Volcanoes with rhyolitic magma commonly erupt explosively, and rhyolitic lava flows are typically of limited extent and have steep margins because the magma is so viscous.{{sfn|Philpotts|Ague|2009|pp=23–26, 59–73}}

Felsic and intermediate magmas that erupt often do so violently, with explosions driven by the release of dissolved gases—typically water vapour, but also [[Chemistry:Carbon dioxide|carbon dioxide]]. Explosively erupted [[Earth:Pyroclastic rock|pyroclastic]] material is called tephra and includes [[Earth:Tuff|tuff]], [[Earth:Agglomerate|agglomerate]] and [[Earth:Ignimbrite|ignimbrite]]. Fine volcanic ash is also erupted and forms ash tuff deposits, which can often cover vast areas.{{sfn|Philpotts|Ague|2009|pp=73–77}}

Because volcanic rocks are mostly fine-grained or glassy, it is much more difficult to distinguish between the different types of extrusive igneous rocks than between different types of intrusive igneous rocks. Generally, the mineral constituents of fine-grained extrusive igneous rocks can only be determined by examination of [[Earth:Thin section|thin section]]s of the rock under a [[Engineering:Optical microscope|microscope]], so only an approximate classification can usually be made in the [[Field research|field]]. Although classification by mineral makeup is preferred by the IUGS, this is often impractical, and chemical classification is done instead using the TAS classification.{{sfn|Philpotts|Ague|2009|pp=139–143}}

==Classification==
{{See|List of rock types}}
[[File:IndianGranite.jpg|thumb|right|Close-up of granite (an intrusive igneous rock) exposed in Chennai, India]]
Igneous rocks are classified according to mode of occurrence, texture, mineralogy, chemical composition, and the geometry of the igneous body.

The classification of the many types of igneous rocks can provide important information about the conditions under which they formed. Two important variables used for the classification of igneous rocks are particle size, which largely depends on the cooling history, and the mineral composition of the rock. [[Chemistry:Feldspar|Feldspar]]s, [[Chemistry:Quartz|quartz]] or [[Chemistry:Feldspathoid|feldspathoid]]s, [[Chemistry:Olivine|olivine]]s, [[Chemistry:Pyroxene|pyroxene]]s, [[Chemistry:Amphibole|amphibole]]s, and [[Chemistry:Mica|mica]]s are all important minerals in the formation of almost all igneous rocks, and they are basic to the classification of these rocks. All other minerals present are regarded as nonessential in almost all igneous rocks and are called ''accessory minerals''. Types of igneous rocks with other essential minerals are very rare, but include carbonatites, which contain essential [[Chemistry:Carbonate|carbonate]]s.{{sfn|Philpotts|Ague|2009|pp=139–143}}

In a simplified classification, igneous rock types are separated on the basis of the type of feldspar present, the presence or absence of [[Chemistry:Quartz|quartz]], and in rocks with no feldspar or quartz, the type of iron or magnesium minerals present. Rocks containing quartz (silica in composition) are ''silica-oversaturated''. Rocks with [[Chemistry:Feldspathoid|feldspathoid]]s are ''silica-undersaturated'', because feldspathoids cannot coexist in a stable association with quartz.{{citation needed|date=October 2021}}

Igneous rocks that have crystals large enough to be seen by the naked eye are called phaneritic; those with crystals too small to be seen are called aphanitic. Generally speaking, phaneritic implies an intrusive origin; aphanitic an extrusive one.{{citation needed|date=October 2021}}

An igneous rock with larger, clearly discernible crystals embedded in a finer-grained matrix is termed [[Earth:Porphyry (geology)|porphyry]]. Porphyritic texture develops when some of the crystals grow to considerable size before the main mass of the magma crystallizes as finer-grained, uniform material.{{citation needed|date=October 2021}}

Igneous rocks are classified on the basis of texture and composition. Texture refers to the size, shape, and arrangement of the mineral grains or crystals of which the rock is composed.{{citation needed|date=October 2021}}

===Texture===
[[File:GabbroRockCreek1.jpg|thumb|Gabbro specimen showing phaneritic texture, from Rock Creek Canyon, eastern Sierra Nevada, California]]
{{main|Earth:Rock microstructure}}
Texture is an important criterion for the naming of volcanic rocks. The [[Earth:Rock microstructure|texture]] of volcanic rocks, including the size, shape, orientation, and distribution of mineral grains and the intergrain relationships, will determine whether the rock is termed a [[Earth:Tuff|tuff]], a [[Earth:Pyroclastic rock|pyroclastic]] lava or a simple [[Earth:Lava|lava]]. However, the texture is only a subordinate part of classifying volcanic rocks, as most often there needs to be chemical information gleaned from rocks with extremely fine-grained [[Earth:Matrix (geology)|groundmass]] or from airfall tuffs, which may be formed from volcanic ash.{{citation needed|date=October 2021}}

Textural criteria are less critical in classifying intrusive rocks where the majority of minerals will be visible to the naked eye or at least using a hand lens, magnifying glass or microscope. Plutonic rocks also tend to be less texturally varied and less prone to showing distinctive structural fabrics. Textural terms can be used to differentiate different intrusive phases of large plutons, for instance [[Earth:Porphyritic|porphyritic]] margins to large intrusive bodies, [[Earth:Porphyry (geology)|porphyry]] stocks and [[Earth:Subvolcanic rock|subvolcanic]] [[Earth:Dike (geology)|dike]]s. Mineralogical classification is most often used to classify plutonic rocks. Chemical classifications are preferred to classify volcanic rocks, with phenocryst species used as a prefix, e.g. "olivine-bearing picrite" or "orthoclase-phyric rhyolite".{{citation needed|date=October 2021}}

===Mineralogical classification===
[[File:Mineralogy igneous rocks EN.svg|thumb|upright=1.35|Basic classification scheme for igneous rocks based on their mineral composition. If the approximate volume fractions of minerals in the rock are known, the rock name and silica content can be read off the diagram. This is not an exact method, because the classification of igneous rocks also depends on other components, yet in most cases it is a good first guess.]]The IUGS recommends classifying igneous rocks by their mineral composition whenever possible. This is straightforward for coarse-grained intrusive igneous rock, but may require examination of thin sections under a microscope for fine-grained volcanic rock, and may be impossible for glassy volcanic rock. The rock must then be classified chemically.<ref>{{Cite journal|last1=Le Bas|first1=M. J.|last2=Streckeisen|first2=A. L.|title=The IUGS systematics of igneous rocks|journal=Journal of the Geological Society|volume=148|issue=5|pages=825–833|doi=10.1144/gsjgs.148.5.0825|bibcode=1991JGSoc.148..825L|year=1991|citeseerx=10.1.1.692.4446|s2cid=28548230}}</ref>

Mineralogical classification of an intrusive rock begins by determining if the rock is ultramafic, a carbonatite, or a lamprophyre. An ultramafic rock contains more than 90% of iron- and magnesium-rich minerals such as hornblende, pyroxene, or olivine, and such rocks have their own classification scheme. Likewise, rocks containing more than 50% carbonate minerals are classified as carbonatites, while lamprophyres are rare ultrapotassic rocks. Both are further classified based on detailed mineralogy.{{sfn|Le Bas|Streckeisen|1991}}

In the great majority of cases, the rock has a more typical mineral composition, with significant quartz, feldspars, or feldspathoids. Classification is based on the percentages of quartz, alkali feldspar, plagioclase, and feldspathoid out of the total fraction of the rock composed of these minerals, ignoring all other minerals present. These percentages place the rock somewhere on the [[Earth:QAPF diagram|QAPF diagram]], which often immediately determines the rock type. In a few cases, such as the diorite-gabbro-anorthite field, additional mineralogical criteria must be applied to determine the final classification.{{sfn|Le Bas|Streckeisen|1991}}

Where the mineralogy of an volcanic rock can be determined, it is classified using the same procedure, but with a modified QAPF diagram whose fields correspond to volcanic rock types.{{sfn|Le Bas|Streckeisen|1991}}

===Chemical classification and petrology===
[[File:Classification extrusive rocks EN.svg|thumb|upright=1.8|Total alkali versus silica classification scheme (TAS) as proposed in Le Maitre's 2002 Igneous Rocks – A classification and glossary of terms<ref>{{cite journal |last1=Shanks III |first1=W.C. Pat |last2=Koski |first2=Randolph A. |last3=Mosier |first3=Dan L. |last4=Schulz |first4=Klaus J. |last5=Morgan |first5=Lisa A. |last6=Slack |first6=John F. |last7=Ridley |first7=W. Ian |last8=Dusel-Bacon |first8=Cynthia |last9=Seal II |first9=Robert R. |last10=Piatak |first10=Nadine M. |editor2-first=Roland |editor2-last=Thurston |editor1-first=W.C. Pat |editor1-last=Shanks |title=Volcanogenic massive sulfide occurrence model: Chapter C in Mineral deposit models for resource assessment |journal=U.S. Geological Survey Scientific Investigations Report |series=Scientific Investigations Report |date=2012 |volume=2010-5070-C |doi=10.3133/sir20105070C |page=237|doi-access=free }}</ref> Blue area is roughly where alkaline rocks plot; yellow area is where subalkaline rocks plot.]]

When it is impractical to classify a volcanic rock by mineralogy, the rock must be classified chemically.

There are relatively few minerals that are important in the formation of common igneous rocks, because the magma from which the minerals crystallize is rich in only certain elements: [[Chemistry:Silicon|silicon]], [[Chemistry:Oxygen|oxygen]], aluminium, [[Chemistry:Sodium|sodium]], [[Chemistry:Potassium|potassium]], [[Chemistry:Calcium|calcium]], iron, and [[Chemistry:Magnesium|magnesium]]. These are the elements that combine to form the [[Chemistry:Silicate minerals|silicate minerals]], which account for over ninety percent of all igneous rocks. The chemistry of igneous rocks is expressed differently for major and minor elements and for trace elements. Contents of major and minor elements are conventionally expressed as weight percent oxides (e.g., 51% SiO<sub>2</sub>, and 1.50% TiO<sub>2</sub>). Abundances of trace elements are conventionally expressed as parts per million by weight (e.g., 420 ppm Ni, and 5.1 ppm Sm). The term "trace element" is typically used for elements present in most rocks at abundances less than 100 ppm or so, but some trace elements may be present in some rocks at abundances exceeding 1,000 ppm. The diversity of rock compositions has been defined by a huge mass of analytical data—over 230,000 rock analyses can be accessed on the web through a site sponsored by the U. S. National Science Foundation (see the External Link to EarthChem).{{citation needed|date=October 2021}}

The single most important component is silica, SiO<sub>2</sub>, whether occurring as quartz or combined with other oxides as feldspars or other minerals. Both intrusive and volcanic rocks are grouped chemically by total silica content into broad categories.
* ''[[Earth:Felsic|Felsic]]'' rocks have the highest content of silica, and are predominantly composed of the ''felsic minerals'' quartz and feldspar. These rocks (granite, rhyolite) are usually light coloured, and have a relatively low density.
* ''Intermediate'' rocks have a moderate content of silica, and are predominantly composed of feldspars. These rocks (diorite, andesite) are typically darker in colour than felsic rocks and somewhat more dense.
* ''[[Earth:Mafic|Mafic]]'' rocks have a relatively low silica content and are composed mostly of [[Chemistry:Pyroxene|pyroxene]]s, [[Chemistry:Olivine|olivine]]s and calcic [[Chemistry:Plagioclase|plagioclase]]. These rocks (basalt, gabbro) are usually dark coloured, and have a higher density than felsic rocks.
* ''Ultramafic'' rock is very low in silica, with more than 90% of mafic minerals (komatiite, [[Earth:Dunite|dunite]]).

This classification is summarized in the following table:

{| cellpadding="2" cellspacing="0" border="1"
|-
|
! style="background:#ffc0c0;" colspan="4"| Composition
|-
! style="background:#ffc0c0;"| Mode of occurrence
| style="background:#c0ffc0;"| Felsic<br />(>63% SiO<sub>2</sub>)
| style="background:#c0ffc0;"| Intermediate<br />(52% to 63% SiO<sub>2</sub>)
| style="background:#c0ffc0;"| Mafic<br />(45% to 52% SiO<sub>2</sub>)
| style="background:#c0ffc0;"| Ultramafic<br />(<45% SiO<sub>2</sub>)
|-
| style="background:#c0ffc0;"| Intrusive
| [[Chemistry:Granite|Granite]]
| [[Earth:Diorite|Diorite]]
| Gabbro
| Peridotite
|-
| style="background:#c0ffc0;"| Extrusive
| [[Earth:Rhyolite|Rhyolite]]
| [[Earth:Andesite|Andesite]]
| [[Earth:Basalt|Basalt]]
| [[Earth:Komatiite|Komatiite]]
|}

The percentage of [[Chemistry:Alkali metal oxide|alkali metal oxide]]s ([[Chemistry:Sodium oxide|Na<sub>2</sub>O]] plus [[Chemistry:Potassium oxide|K<sub>2</sub>O]]) is second only to silica in its importance for chemically classifying volcanic rock. The silica and alkali metal oxide percentages are used to place volcanic rock on the TAS diagram, which is sufficient to immediately classify most volcanic rocks. Rocks in some fields, such as the trachyandesite field, are further classified by the ratio of potassium to sodium (so that potassic trachyandesites are latites and sodic trachyandesites are benmoreites). Some of the more mafic fields are further subdivided or defined by [[Chemistry:Normative mineralogy|normative mineralogy]], in which an idealized mineral composition is calculated for the rock based on its chemical composition. For example, [[Earth:Basanite|basanite]] is distinguished from [[Earth:Tephrite|tephrite]] by having a high normative olivine content.

Other refinements to the basic TAS classification include:
* [[Chemistry:Ultrapotassic igneous rocks|Ultrapotassic]] – rocks containing molar K<sub>2</sub>O/Na<sub>2</sub>O >3.
* [[Earth:Peralkaline rock|Peralkaline]] – rocks containing molar (K<sub>2</sub>O + Na<sub>2</sub>O)/Al<sub>2</sub>O<sub>3</sub> >1.<ref name="blatt-tracy">{{cite book |last1=Blatt |first1=Harvey |last2=Tracy |first2=Robert J. |title=Petrology : igneous, sedimentary, and metamorphic. |date=1996 |publisher=W.H. Freeman |location=New York |isbn=0-7167-2438-3 |page=185 |edition=2nd}}</ref>
* Peraluminous – rocks containing molar (K<sub>2</sub>O + Na<sub>2</sub>O + CaO)/Al<sub>2</sub>O<sub>3</sub> <1.<ref name="blatt-tracy"/>

In older terminology, silica oversaturated rocks were called ''silicic'' or ''acidic'' where the SiO<sub>2</sub> was greater than 66% and the family term ''quartzolite'' was applied to the most silicic. A normative [[Chemistry:Feldspathoid|feldspathoid]] classifies a rock as silica-undersaturated; an example is [[Earth:Nephelinite|nephelinite]].

[[Image:AFM diagram -.svg|thumbnail|right|AFM ternary diagram showing the relative proportions of Na<sub>2</sub>O + K<sub>2</sub>O (A for Alkali earth metals), FeO + Fe<sub>2</sub>O<sub>3</sub> (F), and MgO (M) with arrows showing the path of chemical variation in tholeiitic and calc-alkaline series magmas]]
Magmas are further divided into three series:
* The ''[[Chemistry:Tholeiitic magma series|tholeiitic]]'' series – [[Earth:Basaltic andesite|basaltic andesite]]s and [[Earth:Andesite|andesite]]s.
* The calc-alkaline series – andesites.
* The alkaline series – subgroups of alkaline basalts and the rare, very high potassium-bearing (i.e. [[Earth:Shoshonite|shoshonitic]]) lavas.

The alkaline series is distinguishable from the other two on the TAS diagram, being higher in total alkali oxides for a given silica content, but the tholeiitic and calc-alkaline series occupy approximately the same part of the TAS diagram. They are distinguished by comparing total alkali with iron and magnesium content.{{sfn|Philpotts|Ague|2009|pp=143–146}}

These three magma series occur in a range of plate tectonic settings. Tholeiitic magma series rocks are found, for example, at mid-ocean ridges, [[Earth:Back-arc basin|back-arc basin]]s, oceanic islands formed by hotspots, island arcs and continental [[Earth:Large igneous province|large igneous province]]s.<ref>{{cite web |title=Mafic magma types |url=http://courses.washington.edu/ess439/ESS%20439%20Lecture%2014%20slides.pdf |publisher=University of Washington |access-date=2 December 2020 |archive-date=1 August 2020 |archive-url=https://web.archive.org/web/20200801230945/http://courses.washington.edu/ess439/ESS%20439%20Lecture%2014%20slides.pdf |url-status=dead }}</ref>

All three series are found in relatively close proximity to each other at subduction zones where their distribution is related to depth and the age of the subduction zone. The tholeiitic magma series is well represented above young subduction zones formed by magma from relatively shallow depth. The calc-alkaline and alkaline series are seen in mature subduction zones, and are related to magma of greater depths. Andesite and basaltic andesite are the most abundant volcanic rock in island arc which is indicative of the calc-alkaline magmas. Some island arcs have distributed volcanic series as can be seen in the Japanese island arc system where the volcanic rocks change from tholeiite—calc-alkaline—alkaline with increasing distance from the trench.<ref name=":2">{{Cite journal|last=Gill|first=J.B.|date=1982|title=Andesites: Orogenic andesites and related rocks|journal=Geochimica et Cosmochimica Acta|volume=46|issue=12|pages=2688|doi=10.1016/0016-7037(82)90392-1|issn=0016-7037}}</ref><ref>{{cite journal |last1=Pearce |first1=J |last2=Peate |first2=D |date=1995 |title=Tectonic Implications of the Composition of Volcanic ARC Magmas |journal=Annual Review of Earth and Planetary Sciences |pages=251–285 |volume=23 |issue=1 |doi=10.1146/annurev.ea.23.050195.001343|bibcode=1995AREPS..23..251P }}</ref>

===History of classification===
Some igneous rock names date to before the modern era of geology. For example, ''basalt'' as a description of a particular composition of lava-derived rock dates to [[Biography:Georgius Agricola|Georgius Agricola]] in 1546 in his work ''De Natura Fossilium''.<ref>{{cite journal |last1=Tietz |first1=Olaf |last2=Büchner |first2=Joerg |title=The origin of the term 'basalt' |journal=Journal of Geosciences |date=2018 |volume=63 |issue=4 |pages=295–298 |doi=10.3190/jgeosci.273 |url=http://www.jgeosci.org/content/jgeosci.273_tietz.pdf |access-date=19 August 2020|doi-access=free }}</ref> The word ''granite'' goes back at least to the 1640s and is derived either from French ''granit'' or Italian ''granito'', meaning simply "granulate rock".<ref>{{cite web |last1=Biek |title=Granite |url=https://www.etymonline.com/word/granite |website=Online Etymology Dictionary |publisher=Douglas Harper |access-date=2 December 2020}}</ref> The term ''rhyolite'' was introduced in 1860 by the German traveler and geologist Ferdinand von Richthofen<ref>{{cite journal|last1=Richthofen|first1=Ferdinand Freiherrn von|title=Studien aus den ungarisch-siebenbürgischen Trachytgebirgen|journal=Jahrbuch der Kaiserlich-Königlichen Geologischen Reichsanstalt (Wein) [Annals of the Imperial-Royal Geological Institute of Vienna]|date=1860|volume=11|pages=153–273|url=https://babel.hathitrust.org/cgi/pt?id=uc1.c2537786;view=1up;seq=277|trans-title=Studies of the [[Earth:Trachyte|trachyte]] mountains of Hungarian Transylvania|language=de}}</ref><ref name="OED1">{{cite book | title=Oxford English Dictionary | year=1989 | edition=2nd | volume=13 | page=873 | publisher=[[Organization:Oxford University Press|Oxford University Press]] | location=Oxford | editor1-last=Simpson | editor1-first=John A.  | editor2-last=Weiner | editor2-first=Edmund S. C.}}</ref><ref name="MindMagma">{{cite book | title=Mind Over Magma: The Story of Igneous Petrology | publisher=Princeton University Press | author=Young, Davis A. | year=2003 | pages=117 | isbn=0-691-10279-1}}</ref> The naming of new rock types accelerated in the 19th century and peaked in the early 20th century.<ref name="lebas-etal-2005">{{cite book |last1=Le Maitre |first1=R.W. |last2=Streckeisen |first2=A. |last3=Zanettin |first3=B. |last4=Le Bas |first4=M.J. |last5=Bonin |first5=B. |last6=Bateman |first6=P. |title=Igneous Rocks: A Classification and Glossary of Terms |date=2005 |publisher=Cambridge University Press |isbn=978-0-521-66215-4 |pages=46–48}}</ref>

Much of the early classification of igneous rocks was based on the geological age and occurrence of the rocks. However, in 1902, the American petrologists Charles Whitman Cross, Joseph P. Iddings, Louis V. Pirsson, and Henry Stephens Washington proposed that all existing classifications of igneous rocks should be discarded and replaced by a "quantitative" classification based on chemical analysis. They showed how vague, and often unscientific, much of the existing terminology was and argued that as the chemical composition of an igneous rock was its most fundamental characteristic, it should be elevated to prime position.<ref name=EB1911>{{EB1911|wstitle=Petrology |volume=21 |page=330 |inline=1 |first=John Smith |last=Flett}}</ref><ref name="cipw">{{cite book |last1=Cross |first1=C.W. |last2=Iddings |first2=J.P. |last3=Pirsson |first3=L.V. |last4=Washington |first4=H.S. |year=1903 |title=Quantitative Classification of Igneous Rocks |location=Chicago |publisher=University of Chicago Press}}</ref>

Geological occurrence, structure, mineralogical constitution—the hitherto accepted criteria for the discrimination of rock species—were relegated to the background. The completed rock analysis is first to be interpreted in terms of the rock-forming minerals which might be expected to be formed when the magma crystallizes, e.g., quartz feldspars, [[Chemistry:Olivine|olivine]], akermannite, [[Chemistry:Feldspathoid|Feldspathoid]]s, [[Chemistry:Magnetite|magnetite]], [[Chemistry:Corundum|corundum]], and so on, and the rocks are divided into groups strictly according to the relative proportion of these minerals to one another.<ref name=EB1911/> This new classification scheme created a sensation, but was criticized for its lack of utility in fieldwork, and the classification scheme was abandoned by the 1960s. However, the concept of normative mineralogy has endured, and the work of Cross and his coinvestigators inspired a flurry of new classification schemes.<ref>{{cite journal |last1=Oldroyd |first1=David |last2=Young |first2=Davis |title=Of the American Quantitative Igneous Rock Classification: Part 5 |journal=Earth Sciences History |date=1 January 2012 |volume=31 |issue=1 |pages=1–41 |doi=10.17704/eshi.31.1.17660412784m64r4|bibcode=2012ESHis..31....1Y }}</ref>

Among these was the classification scheme of M.A. Peacock, which divided igneous rocks into four series: the alkalic, the alkali-calcic, the calc-alkali, and the calcic series.<ref>{{cite journal |last1=Peacock |first1=M. A. |title=Classification of Igneous Rock Series |journal=The Journal of Geology |date=1 January 1931 |volume=39 |issue=1 |pages=54–67 |doi=10.1086/623788|bibcode=1931JG.....39...54P |s2cid=140563237 }}</ref> His definition of the alkali series, and the term calc-alkali, continue in use as part of the widely used{{sfn|Philpotts|Ague|2009|p=143}} Irvine-Barager classification,<ref>{{cite journal |last1=Irvine |first1=T. N. |last2=Baragar |first2=W. R. A. |title=A Guide to the Chemical Classification of the Common Volcanic Rocks |journal=Canadian Journal of Earth Sciences |date=6 February 2011 |volume=8 |issue=5 |pages=523–548 |doi=10.1139/e71-055|bibcode=1971CaJES...8..523I }}</ref> along with W.Q. Kennedy's tholeiitic series.<ref>{{cite journal |last1=Kennedy |first1=W. Q. |title=Trends of differentiation in basaltic magmas |journal=American Journal of Science |date=1 March 1933 |volume=s5-25 |issue=147 |pages=239–256 |doi=10.2475/ajs.s5-25.147.239|bibcode=1933AmJS...25..239K }}</ref>

By 1958, there were some 12 separate classification schemes and at least 1637 rock type names in use. In that year, Albert Streckeisen wrote a review article on igneous rock classification that ultimately led to the formation of the IUGG Subcommission of the Systematics of Igneous Rocks. By 1989 a single system of classification had been agreed upon, which was further revised in 2005. The number of recommended rock names was reduced to 316. These included a number of new names promulgated by the Subcommission.<ref name="lebas-etal-2005"/>

==Origin of magmas==
The Earth's crust averages about {{convert|35|km}} thick under the [[Earth:Continental crust|continents]], but averages only some {{convert|7–10|km}} beneath the [[Earth:Oceanic crust|oceans]]. The continental crust is composed primarily of sedimentary rocks resting on a crystalline ''[[Earth:Basement (geology)|basement]]'' formed of a great variety of metamorphic and igneous rocks, including [[Earth:Granulite|granulite]] and granite. Oceanic crust is composed primarily of basalt and gabbro. Both continental and oceanic crust rest on peridotite of the mantle.{{citation needed|date=October 2021}}

Rocks may melt in response to a decrease in pressure, to a change in composition (such as an addition of water), to an increase in temperature, or to a combination of these processes.{{citation needed|date=October 2021}}

Other mechanisms, such as melting from a [[Astronomy:Impact event|meteorite impact]], are less important today, but impacts during the [[Earth:Accretion (geology)|accretion]] of the Earth led to extensive melting, and the outer several hundred kilometers of our early Earth was probably an ocean of magma. Impacts of large meteorites in the last few hundred million years have been proposed as one mechanism responsible for the extensive basalt magmatism of several large igneous provinces.{{citation needed|date=October 2021}}

===Decompression===<!-- This section is linked from Basalt -->
Decompression melting occurs because of a decrease in pressure.<ref name=Wilson>{{cite book |title=Understanding the Earth |author1=Geoff C. Brown |author2=C. J. Hawkesworth |author3=R. C. L. Wilson |page=93 |url=https://books.google.com/books?id=Kgk4AAAAIAAJ&pg=PA93 |isbn=0-521-42740-1 |edition=2nd |year=1992 |publisher=Cambridge University Press}}</ref>

The [[Chemistry:Solidus|solidus]] temperatures of most rocks (the temperatures below which they are completely solid) increase with increasing pressure in the absence of water. Peridotite at depth in the [[Earth:Earth's mantle|Earth's mantle]] may be hotter than its solidus temperature at some shallower level. If such rock rises during the [[Physics:Mantle convection|convection]] of solid mantle, it will cool slightly as it expands in an [[Physics:Adiabatic process|adiabatic process]], but the cooling is only about 0.3&nbsp;°C per kilometer. Experimental studies of appropriate peridotite samples document that the solidus temperatures increase by 3&nbsp;°C to 4&nbsp;°C per kilometer. If the rock rises far enough, it will begin to melt. Melt droplets can coalesce into larger volumes and be intruded upwards. This process of melting from the upward movement of solid mantle is critical in the evolution of the Earth.{{citation needed|date=October 2021}}

Decompression melting creates the ocean crust at mid-ocean ridges. It also causes volcanism in intraplate regions, such as Europe, Africa and the Pacific sea floor. There, it is variously attributed either to the rise of [[Earth:Mantle plume|mantle plume]]s (the "Plume hypothesis") or to intraplate extension (the "Plate hypothesis").<ref name=Foulger>{{cite book |title=Plates vs. Plumes: A Geological Controversy |author=Foulger, G.R. |url=http://www.wiley.com/WileyCDA/WileyTitle/productCd-1405161485.html |year=2010 |isbn=978-1-4051-6148-0 |publisher=Wiley-Blackwell}}</ref>

===Effects of water and carbon dioxide===
The change of rock composition most responsible for the creation of magma is the addition of water. Water lowers the solidus temperature of rocks at a given pressure. For example, at a depth of about 100 kilometers, peridotite begins to melt near 800&nbsp;°C in the presence of excess water, but near or above about 1,500&nbsp;°C in the absence of water.<ref>{{cite journal | last1 = Grove | first1 = T. L. | last2 = Chatterjee | first2 = N. | last3 = Parman | first3 = S. W. | last4 = Medard | first4 = E. | year = 2006 | title = The influence of H<sub>2</sub>O on mantle wedge melting. | journal = Earth and Planetary Science Letters | volume = 249 | issue = 1–2| pages = 74–89 | doi = 10.1016/j.epsl.2006.06.043 | bibcode = 2006E&PSL.249...74G }}</ref> Water is driven out of the oceanic [[Earth:Lithosphere|lithosphere]] in subduction zones, and it causes melting in the overlying mantle. Hydrous magmas composed of basalt and andesite are produced directly and indirectly as results of dehydration during the subduction process. Such magmas, and those derived from them, build up [[Earth:Island arc|island arc]]s such as those in the Pacific Ring of Fire. These magmas form rocks of the calc-alkaline series, an important part of the [[Earth:Continental crust|continental crust]].{{citation needed|date=October 2021}}

The addition of [[Chemistry:Carbon dioxide|carbon dioxide]] is relatively a much less important cause of magma formation than the addition of water, but genesis of some [[Chemistry:Normative mineralogy|silica-undersaturated]] magmas has been attributed to the dominance of carbon dioxide over water in their mantle source regions. In the presence of carbon dioxide, experiments document that the peridotite solidus temperature decreases by about 200&nbsp;°C in a narrow pressure interval at pressures corresponding to a depth of about 70&nbsp;km. At greater depths, carbon dioxide can have more effect: at depths to about 200&nbsp;km, the temperatures of initial melting of a carbonated peridotite composition were determined to be 450&nbsp;°C to 600&nbsp;°C lower than for the same composition with no carbon dioxide.<ref>{{cite journal | last1 = Dasgupta | first1 = R. | last2 = Hirschmann | first2 = M. M. | year = 2007 | title = Effect of variable carbonate concentration on the solidus of mantle peridotite | journal = American Mineralogist | volume = 92 | issue = 2–3| pages = 370–379 | doi = 10.2138/am.2007.2201 | bibcode = 2007AmMin..92..370D | s2cid = 95932394 }}</ref> Magmas of rock types such as [[Earth:Nephelinite|nephelinite]], carbonatite, and [[Earth:Kimberlite|kimberlite]] are among those that may be generated following an influx of carbon dioxide into mantle at depths greater than about 70&nbsp;km.{{citation needed|date=October 2021}}

===Temperature increase===
Increase in temperature is the most typical mechanism for formation of magma within continental crust. Such temperature increases can occur because of the upward intrusion of magma from the mantle. Temperatures can also exceed the solidus of a crustal rock in continental crust thickened by compression at a plate boundary. The plate boundary between the Indian and Asian continental masses provides a well-studied example, as the [[Place:Tibetan Plateau|Tibetan Plateau]] just north of the boundary has crust about 80 kilometers thick, roughly twice the thickness of normal continental crust. Studies of electrical resistivity deduced from [[Physics:Magnetotellurics|magnetotelluric data]] have detected a layer that appears to contain [[Chemistry:Silicate|silicate]] melt and that stretches for at least 1,000 kilometers within the middle crust along the southern margin of the Tibetan Plateau.<ref>{{cite journal | last1 = Unsworth | first1 = M. J. | display-authors = etal | year = 2005 | title =  Crustal rheology of the Himalaya and Southern Tibet inferred from magnetotelluric data| journal = Nature | volume = 438 | issue = 7064| pages = 78–81 | doi = 10.1038/nature04154 | pmid = 16267552 | bibcode = 2005Natur.438...78U | s2cid = 4359642 }}</ref> Granite and [[Earth:Rhyolite|rhyolite]] are types of igneous rock commonly interpreted as products of the melting of continental crust because of increases in temperature. Temperature increases also may contribute to the melting of [[Earth:Lithosphere|lithosphere]] dragged down in a subduction zone.{{citation needed|date=October 2021}}

===Magma evolution===
[[File:Fractional crystallization.svg|thumb|upright=1.8|Schematic diagrams showing the principles behind fractional crystallisation in a magma. While cooling, the magma evolves in composition because different minerals crystallize from the melt. '''1''': olivine crystallizes; '''2''': olivine and pyroxene crystallize; '''3''': pyroxene and plagioclase crystallize; '''4''': plagioclase crystallizes. At the bottom of the magma reservoir, a cumulate rock forms.]]
:{{main|Chemistry:Igneous differentiation}}
Most magmas are fully melted only for small parts of their histories. More typically, they are mixes of melt and crystals, and sometimes also of gas bubbles. Melt, crystals, and bubbles usually have different densities, and so they can separate as magmas evolve.

As magma cools, minerals typically crystallize from the melt at different temperatures (fractional crystallization). As minerals crystallize, the composition of the residual melt typically changes. If crystals separate from the melt, then the residual melt will differ in composition from the parent magma. For instance, a magma of gabbroic composition can produce a residual melt of [[Chemistry:Granite|granitic]] composition if early formed crystals are separated from the magma. Gabbro may have a [[Physics:Liquidus|liquidus]] temperature near 1,200&nbsp;°C, and the derivative granite-composition melt may have a liquidus temperature as low as about 700&nbsp;°C. [[Chemistry:Incompatible element|Incompatible element]]s are concentrated in the last residues of magma during fractional crystallization and in the first melts produced during partial melting: either process can form the magma that crystallizes to [[Earth:Pegmatite|pegmatite]], a rock type commonly enriched in incompatible elements. [[Earth:Bowen's reaction series|Bowen's reaction series]] is important for understanding the idealised sequence of fractional crystallisation of a magma. [[Chemistry:Clinopyroxene thermobarometry|Clinopyroxene thermobarometry]] is used to determine temperature and pressure conditions at which magma differentiation occurred for specific igneous rocks. {{citation needed|date=October 2021}}

Magma composition can be determined by processes other than partial melting and fractional crystallization. For instance, magmas commonly interact with rocks they intrude, both by melting those rocks and by reacting with them. Magmas of different compositions can mix with one another. In rare cases, melts can separate into two immiscible melts of contrasting compositions.{{citation needed|date=October 2021}}

==Etymology==

* The word ''igneous'' rock means ''composed of fire''. and is derived from the [[Social:Latin|Latin]] root words of ''igni-'',<ref>{{cite web|title=igneous|website=Dictionary.com|language=en|url=https://www.dictionary.com/browse/igneous|access-date=15 October 2022|url-status=live|archive-url=https://web.archive.org/web/20221015092537/https://www.dictionary.com/browse/igneous|archive-date=15 October 2022}}</ref> meaning ''fire'', and ''-eous''<ref>{{cite web|title=-eous|website=Dictionary.com|language=en|url=https://www.dictionary.com/browse/-eous|access-date=15 October 2022|url-status=live|archive-url=https://web.archive.org/web/20221015092751/https://www.dictionary.com/browse/-eous|archive-date=15 October 2022}}</ref> meaning ''composed of''.
* The word ''[[Earth:Volcanic rock|volcanic rock]]'' is derived from the [[Social:Latin|Latin]] root words of ''[[Biology:Vulcan (mythology)|Vulcan]]'',<ref>{{cite web|title=Volvano|website=Dictionary.com|language=en|url=https://www.dictionary.com/browse/volcano|access-date=15 October 2022|url-status=live|archive-url=https://web.archive.org/web/20221015120740/https://www.dictionary.com/browse/volcano|archive-date=15 October 2022}}
</ref> the [[History:Ancient Rome|Roman]] the god of fire, and ''-ic'',<ref>{{cite web|title=ic|website=Dictionary.com|language=en|url=https://www.dictionary.com/browse/ic|access-date=15 October 2022|url-status=live|archive-url=https://web.archive.org/web/20221015094717/https://www.dictionary.com/browse/ic|archive-date=15 October 2022}}</ref> meaning ''having some characteristics of''.
* The word ''plutonic'' rock, another name for [[Earth:Intrusive rock|intrusive]] igneous rock, is derived from the [[Social:Latin|Latin]] root words of ''Pluto'',<ref>{{cite web|title=Pluto|website=Dictionary.com|language=en|url=https://www.dictionary.com/browse/plutonic|access-date=15 October 2022|url-status=live|archive-url=https://web.archive.org/web/20221015095057/https://www.dictionary.com/browse/plutonic|archive-date=15 October 2022}}</ref> the [[History:Ancient Rome|Roman]] god of the underworld, and ''-ic'',<ref>{{cite web|title=ic|website=Dictionary.com|language=en|url=https://www.dictionary.com/browse/ic|access-date=15 October 2022|url-status=live|archive-url=https://web.archive.org/web/20221015094717/https://www.dictionary.com/browse/ic|archive-date=15 October 2022}}</ref> meaning ''having some characteristics of''.

== Gallery ==
<gallery mode=packed>
File:Kanaga Volcano (22432739869).jpg|[[Earth:Mount Kanaga|Kanaga]] volcano in the [[Biography:Aleutian Islands|Aleutian Islands]] with a 1906 lava flow in the foreground
File:Molten Lava in Pahoehoe Skylight.jpg|A "skylight" hole, about {{cvt|6|m}} across, in a solidified lava crust reveals molten lava below (flowing towards the top right) in an eruption of [[Earth:Kīlauea|Kīlauea]] in Hawaii
File:"This means something. This is important" (19967592275).jpg|[[Earth:Devils Tower|Devils Tower]], an eroded laccolith in the Black Hills of Wyoming
File:Happy Anniversary Hawaii (14802198589).jpg| A cascade of molten lava flowing into Aloi Crater during the 1969–1971 Mauna Ulu eruption of Kilauea volcano
File:Columnar jointing in the Alcantara Gorge, Sicily.jpg|[[Earth:Columnar jointing|Columnar jointing]] in the Alcantara Gorge, [[Place:Sicily|Sicily]]
File:Cretaceous sedimentary rocks intruded by a Miocene granite laccolith.jpg|A laccolith of granite (light-coloured) that was intruded into older sedimentary rocks (dark-coloured) at Cuernos del Paine, Torres del Paine National Park, Chile
File:Multiple Igneous Intrusion Phases Kosterhavet Sweden.jpg| An igneous intrusion cut by a [[Earth:Pegmatite|pegmatite]] dike, which in turn is cut by a dolerite dike
</gallery>

==See also==
* {{annotated link|Earth:List of rock types}}
* {{annotated link|Earth:Metamorphic rock}}
* {{annotated link|Earth:Migmatite}}
* {{annotated link|Earth:Petrology}}
* {{annotated link|Earth:Sedimentary rock}}

==Notes==
{{reflist|group=note}}

==References==
{{reflist}}

==External links==
* [http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Notes/igneous_rocks.html USGS Igneous Rocks] {{Webarchive|url=https://web.archive.org/web/20130221075708/http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Notes/igneous_rocks.html |date=21 February 2013 }}
* [https://web.archive.org/web/20080510070325/http://geol.lsu.edu/henry/Geology3041/lectures/02IgneousClassify/IUGS-IgneousClassFlowChart.htm Igneous rock classification flowchart]
* [https://web.archive.org/web/20120113152818/http://geology.cnsm.ad.csulb.edu/people/bperry/IgneousRocksTour/IntroToIgneousRocks.html Igneous Rocks Tour, an introduction to Igneous Rocks]
* [https://web.archive.org/web/20130502230620/http://www.utdallas.edu/~aiken/SHAKEBAKE/rockclassification.pdf The IUGS systematics of igneous rocks]

{{Igneous rocks}}

{{DEFAULTSORT:Igneous Rock}}
[[Category:Volcanology]]

{{Sourceattribution|Igneous rock}}