View source for Komatiite

{{short description|Magnesium-rich igneous rock}}
[[File:Komatiite Lava in South Africa - CSIRO ScienceImage 11033.jpg|thumb|Komatiite lava at the type locality in the Komati Valley, Barberton Mountainland, South Africa, showing the distinctive "spinifex texture" formed by dendritic plates of olivine (scale shown by a hammer on the right edge of photo)]]

'''Komatiite''' {{IPAc-en|k|oʊ|ˈ|m|ɑː|t|i|ˌ|aɪ|t}} is a type of [[ultramafic]] [[mantle (geology)|mantle]]-derived [[volcanic rock]] defined as having crystallised from a [[lava]] of at least 18 wt% [[magnesium oxide]] (MgO).<ref>Le Bas, M. J. 2000. IUGS reclassification of the high-Mg and picritic volcanic rocks. Journal of Petrology, 41(10), 1467–1470. https://doi.org/10.1093/petrology/41.10.1467</ref> It is classified as a 'picritic rock'. Komatiites have low [[silicon]], [[potassium]] and [[aluminium]], and high to extremely high [[magnesium]] content. Komatiite was named for its [[Type locality (geology)|type locality]] along the [[Komati River]] in South Africa,<ref>Viljoen, M. J., & Viljoen, R. P. 1969a. Evidence for the existence of a mobile extrusive peridotitic magma from the Komati Formation of the Onvernacht Group. Geological Survey of South Africa, Special Publication, 21, 87 – 112.</ref> and frequently displays [[Triodia (grass)|spinifex]] texture composed of large dendritic plates of [[olivine]] and [[pyroxene]].<ref>Arndt, N., Lesher, C. M., & Barnes, S. J. 2008. Komatiite. Cambridge: Cambridge University Press.</ref>

Komatiites are rare rocks; almost all komatiites were formed during the [[Archean|Archaean]] Eon (4.03–2.5 billion years ago), with few younger ([[Proterozoic]] or [[Phanerozoic]]) examples known. This restriction in age is thought to be due to cooling of the mantle, which may have been {{cvt|100–250|C|F}} hotter during the Archaean.<ref>Davies, G. F. 1999. Plates, Plumes and Mantle Convection. Cambridge: Cambridge University Press.</ref><ref>Herzberg, C., Condie, K., & Korenaga, J. 2010. Thermal history of the Earth and its petrological expression. Earth and Planetary Science Letters, 292(1–2), 79–88. https://doi.org/10.1016/j.epsl.2010.01.022</ref> The early Earth had much higher heat production, due to the residual heat from [[planetary accretion]], as well as the greater abundance of [[radioactive]] isotopes, particularly shorter lived ones like [[uranium 235]] which produce more [[decay heat]]. Lower temperature mantle melts such as [[basalt]] and [[Picrite basalt|picrite]] have essentially replaced komatiites as an eruptive lava on the Earth's surface.

Geographically, komatiites are predominantly restricted in distribution to the Archaean [[shield (geology)|shield]] areas, and occur with other [[Ultramafic rock|ultramafic]] and high-magnesian [[mafic]] volcanic rocks in Archaean [[greenstone belt]]s.  The youngest komatiites are from the island of [[Gorgona, Colombia|Gorgona]] on the Caribbean [[oceanic plateau]] off the Pacific coast of Colombia, and a rare example of Proterozoic komatiite is found in the [[Winnipegosis komatiite belt]] in [[Manitoba]], Canada.

== Petrology ==
[[File:KomatiiteCanada 682By512.jpg|thumb|right|Komatiite sample collected from the [[Abitibi greenstone belt]] near [[Englehart, Ontario]], Canada. Specimen is 9 cm wide.  Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample.]]
[[Magmas]] of komatiitic compositions have a very high [[melting point]], with calculated eruption temperatures up to, and possibly in excess of 1600&nbsp;°C.<ref>Nisbet, E. G., Cheadle, M. J., Arndt, Nicholas T., & Bickle, M. J. 1993. Constraining the potential temperature of the Archaean mantle: A review of the evidence from komatiites. Lithos, 30(3–4), 291–307. https://doi.org/10.1016/0024-4937(93)90042-B</ref><ref>Robin-Popieul, C. C. M., Arndt, N. T., [[Catherine Chauvel|Chauvel, C.]], Byerly, G. R., Sobolev, A. V., & Wilson, A. 2012. A new model for Barberton komatiites: Deep critical melting with high melt retention. Journal of Petrology, 53(11), 2191–2229. https://doi.org/10.1093/petrology/egs042</ref><ref>Sossi, P. A., Eggins, S. M., Nesbitt, R. W., Nebel, O., [[Janet Hergt|Hergt, J. M.]], Campbell, I. H., O'Neill, H. St. C., Van Kranendonk, M., & Davies, R. D. 2016. Petrogenesis and geochemistry of Archean Komatiites. Journal of Petrology, 57(1), 147–184. https://doi.org/10.1093/petrology/egw004</ref><ref>Waterton, P., Pearson, D. G., Kjarsgaard, B., Hulbert, L., Locock, A., Parman, S. W., & Davis, B. 2017. Age, Origin, and Thermal Evolution of the ultra-fresh ~1.9 Ga Winnipegosis Komatiites, Manitoba, Canada. Lithos, 268–271, 114–130. https://doi.org/10.1016/j.lithos.2016.10.033</ref>  [[Basalt]]ic [[lava]]s normally have eruption temperatures of about 1100 to 1250&nbsp;°C.  The higher melting temperatures required to produce komatiite have been attributed to the presumed higher [[geothermal gradient]]s in the Archaean Earth.

Komatiitic lava was extremely fluid when it erupted (possessing the [[viscosity]] close to that of water but with the density of rock). Compared to the basaltic lava of the [[Hawaiian eruption|Hawaiian]] [[Mantle plume|plume]] basalts at ~1200&nbsp;°C, which flows the way [[treacle]] or honey does, the komatiitic lava would have flowed swiftly across the surface, leaving extremely thin lava flows (down to 10&nbsp;mm thick). The major komatiitic sequences preserved in Archaean rocks are thus considered to be [[lava tubes]], ponds of lava etc., where the komatiitic lava accumulated.

Komatiite chemistry is different from that of basaltic and other common mantle-produced magmas, because of differences in degrees of [[partial melting]]. Komatiites are considered to have been formed by high degrees of partial melting, usually greater than 50%, and hence have high MgO with low K<sub>2</sub>O and other [[incompatible element]]s.

There are two geochemical classes of komatiite; aluminium undepleted komatiite (AUDK) (also known as Group I komatiites) and aluminium depleted komatiite (ADK) (also known as Group II komatiites), defined by their Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> ratios. These two classes of komatiite are often assumed to represent a real [[Petrology|petrological]] source difference between the two types related to depth of melt generation. Al-depleted komatiites have been modeled by melting experiments as being produced by high degrees of partial melting at high pressure where [[garnet]] in the source is not melted, whereas Al-undepleted komatiites are produced by high degrees of partial melts at lesser depth. However, recent studies of fluid inclusions in [[Chromium|chrome]] [[Spinel group|spinels]] from the cumulate zones of komatiite flows have shown that a single komatiite flow can be derived from the mixing of parental magmas with a range of Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> ratios, calling into question this interpretation of the formations of the different komatiite groups.<ref>{{cite journal|title=Chrome spinel-hosted melt inclusions in Paleoproterozoic primitive volcanic rocks, northern Finland: Evidence for coexistence and mixing of komatiitic and picritic magmas|doi=10.1016/j.chemgeo.2013.02.009|year=2013|last1=Hanski|first1=E.|last2=Kamenetsky|first2=V.S.|journal=Chemical Geology|volume=343|pages=25–37|bibcode=2013ChGeo.343...25H}}</ref> Komatiites probably form in extremely hot mantle plumes<ref>{{cite journal |last1=McDonough |first1=W. F. |last2=Ireland |first2=T. R. |title=Intraplate origin of komatiites inferred from trace elements in glass inclusions |journal=Nature |date=September 1993 |volume=365 |issue=6445 |pages=432–434 |doi=10.1038/365432a0|bibcode=1993Natur.365..432M |s2cid=4257168 }}</ref> or in Archaean subduction zones.<ref>{{cite journal |last1=Parman |first1=S. W. |title=A subduction origin for komatiites and cratonic lithospheric mantle |journal=South African Journal of Geology |date=1 June 2004 |volume=107 |issue=1–2 |pages=107–118 |doi=10.2113/107.1-2.107|bibcode=2004SAJG..107..107P |hdl=11427/24075 |hdl-access=free }}</ref>

[[Boninite]] magmatism is similar to komatiite magmatism but is produced by fluid-fluxed melting above a [[subduction zone]]. Boninites with 10–18% MgO tend to have higher [[Incompatible element|large-ion lithophile elements]] (LILE: [[Barium|Ba]], [[Rubidium|Rb]], [[Strontium|Sr]]) than komatiites.

== Mineralogy ==
[[File:KomatiiteGraph.jpg|thumb|right|upright=1.4|Graph of komatiite geochemistry MgO% vs Cr ppm, from basal flows, Wannaway, Western Australia]]
The pristine volcanic mineralogy of komatiites is composed of forsteritic olivine (Fo90 and upwards), calcic and often chromian [[pyroxene]], [[anorthite]] (An85 and upwards) and [[chromite]].

A considerable population of komatiite examples show a [[cumulate rocks|cumulate texture]] and [[Geomorphology|morphology]]. The usual cumulate [[mineralogy]] is highly magnesium rich [[forsterite]] olivine, though chromian pyroxene cumulates are also possible (though rarer).

Volcanic rocks rich in magnesium may be produced by accumulation of olivine [[phenocrysts]] in basalt melts of normal chemistry: an example is [[picrite]]. Part of the evidence that komatiites are not magnesium-rich simply because of cumulate olivine is textural: some contain spinifex [[Texture (geology)|texture]], a texture attributable to rapid [[crystallization]] of the olivine in a thermal gradient in the upper part of a lava flow. "Spinifex" texture is named after the common name for the Australian grass ''[[Triodia (grass)|Triodia]]'',<ref name="Dostal2008">{{cite journal | url=https://journals.lib.unb.ca/index.php/GC/article/view/11074/11722 | title=Igneous Rock Associations 10. Komatiites | last1=Dostal | first1=J. | journal=Geoscience Canada | year=2008 | volume=35 | issue=1}}</ref> which grows in clumps with similar shapes.

Another line of evidence is that the MgO content of olivines formed in komatiites is toward the nearly pure MgO forsterite composition, which can only be achieved in bulk by crystallisation of olivine from a highly magnesian melt.

The rarely preserved flow top [[breccia]] and pillow margin zones in some komatiite flows are essentially volcanic glass, [[quenched]] in contact with overlying water or air. Because they are rapidly cooled, they represent the liquid composition of the komatiites, and thus record an [[anhydrous]] MgO content of up to 32% MgO. Some of the highest magnesian komatiites with clear textural preservation are those of the [[Barberton belt]] in South Africa, where liquids with up to 34% MgO can be inferred using bulk rock and olivine compositions.

The mineralogy of a komatiite varies systematically through the typical [[stratigraphic section]] of a komatiite flow and reflects magmatic processes which komatiites are susceptible to during their eruption and cooling. The typical mineralogical variation is from a flow base composed of olivine cumulate, to a spinifex textured zone composed of bladed olivine and ideally a pyroxene spinifex zone and olivine-rich chill zone on the upper eruptive rind of the flow unit.

Primary (magmatic) mineral species also encountered in komatiites include olivine, the pyroxenes [[augite]], [[pigeonite]] and [[bronzite]], [[plagioclase]], [[chromite]], [[ilmenite]] and rarely pargasitic [[amphibole]]. Secondary (metamorphic) minerals include [[serpentine group|serpentine]], [[Chlorite group|chlorite]], amphibole, sodic plagioclase, [[quartz]], iron oxides and rarely [[phlogopite]], [[baddeleyite]], and [[pyrope]] or [[hydrogrossular]] [[garnet]].

== Metamorphism ==
{{Unreferenced section|date=November 2020}}
All known komatiites have been [[Metamorphism|metamorphosed]], therefore should technically be termed 'metakomatiite' though the prefix meta is inevitably assumed. Many komatiites are highly altered and [[serpentinite|serpentinized]] or [[carbonated]] from metamorphism and [[metasomatism]]. This results in significant changes to the mineralogy and the texture.

=== Hydration vs. carbonation ===
The metamorphic mineralogy of ultramafic rocks, particularly komatiites, is only partially controlled by composition. The character of the [[connate fluids]] which are present during low temperature metamorphism whether [[Metamorphism#Prograde and retrograde|prograde]] or [[Metamorphism#Prograde and retrograde|retrograde]] control the metamorphic assemblage of a metakomatiite (''hereafter the prefix meta- is assumed'').

The factor controlling the mineral assemblage is the [[partial pressure]] of [[carbon dioxide]] within the metamorphic fluid, called the XCO<sub>2</sub>. If XCO<sub>2</sub> is above 0.5, the metamorphic reactions favor formation of [[talc]], [[magnesite]] (magnesium carbonate), and [[tremolite]] amphibole. These are classed as [[talc carbonate|talc-carbonation]] reactions. Below XCO<sub>2</sub> of 0.5, metamorphic reactions in the presence of water favor production of [[serpentinite]].

There are thus two main classes of metamorphic komatiite; carbonated and hydrated. Carbonated komatiites and peridotites form a series of rocks dominated by the minerals chlorite, talc, magnesite or [[Dolomite (mineral)|dolomite]] and tremolite. Hydrated metamorphic rock assemblages are dominated by the minerals chlorite, [[serpentine group|serpentine]]-[[antigorite]] and [[brucite]]. Traces of talc, tremolite and dolomite may be present, as it is very rare that no carbon dioxide is present in metamorphic fluids. At higher metamorphic grades, [[anthophyllite]], [[enstatite]], olivine and [[diopside]] dominate as the rock mass dehydrates.

=== Mineralogic variations in komatiite flow facies ===
Komatiite tends to [[Fractional crystallization (geology)|fractionate]] from high-magnesium compositions in the flow bases where olivine cumulates dominate, to lower magnesium compositions higher up in the flow. Thus, the current metamorphic mineralogy of a komatiite will reflect the chemistry, which in turn represents an inference as to its volcanological [[facies]] and stratigraphic position.

Typical metamorphic mineralogy is [[tremolite]]-[[Chlorite group|chlorite]], or [[talc]]-chlorite mineralogy in the upper spinifex zones. The more magnesian-rich olivine-rich flow base facies tend to be free from tremolite and chlorite mineralogy and are dominated by either [[serpentine group|serpentine]]-[[brucite]] +/- [[anthophyllite]] if hydrated, or talc-[[magnesite]] if carbonated. The upper flow facies tend to be dominated by talc, chlorite, tremolite, and other magnesian amphiboles ([[anthophyllite]], [[cummingtonite]], [[gedrite]], etc.).

For example, the typical flow facies (see below) may have the following mineralogy;
{| border="0" cellpadding="2"
|+
|-
! Facies: !! Hydrated !! Carbonated
|-
! A1
| Chlorite-tremolite  || Talc-chlorite-tremolite
|-
! A2
| Serpentine-tremolite-chlorite || Talc-tremolite-chlorite
|-
! A3
| Serpentine-chlorite || Talc-magnesite-tremolite-chlorite
|-
! B1
| Serpentine-chlorite-anthophyllite || Talc-magnesite
|-
! B2
| Massive serpentine-brucite || Massive talc-magnesite
|-
! B3
| Serpentine-brucite-chlorite || Talc-magnesite-tremolite-chlorite
|}

== Geochemistry ==
Komatiite can be classified according to the following [[IUGS]] geochemical criteria:<ref>{{cite journal |last1=Le Bas |first1=M. |last2=Streckeisen |first2=A. |title=The IUGS systematics of igneous rocks |journal=Journal of the Geological Society, London |date=1991 |volume=148 |page=825-833 |doi=10.1144/gsjgs.148.5.0825}}</ref>

* SiO<sub>2</sub> less than 52 [[wt%]]
* MgO more than 18 wt%
* K<sub>2</sub>O + Na<sub>2</sub>O less than 1 wt%
* TiO<sub>2</sub> less than 1 wt%

When meeting the above, but the TiO<sub>2</sub> is more than 1 wt%, it is classified as [[meimechite]].

A similar high-Mg volcanic rock is [[boninite]], having 52–63 wt% SiO<sub>2</sub>, more than 8 wt% MgO and less than 0.5 wt% TiO<sub>2</sub>.

The above geochemical classification must be the essentially unaltered magma chemistry and not the result of [[cumulate rocks|crystal accumulation]] (as in [[peridotite]]). Through a typical komatiite flow sequence the chemistry of the rock will change according to the internal fractionation which occurs during eruption. This tends to lower MgO, Cr, Ni, and increase Al, K<sub>2</sub>O, Na, CaO and SiO<sub>2</sub> toward the top of the flow.

Rocks rich in MgO, K<sub>2</sub>O, Ba, Cs, and Rb may be [[lamprophyre]]s, [[kimberlite]]s or other rare ultramafic, potassic or [[ultrapotassic]] rocks.

== Morphology and occurrence ==
Komatiites often show [[pillow lava]] structure, autobrecciated upper margins consistent with underwater eruption forming a rigid upper skin to the lava flows. Proximal volcanic facies are thinner and interleaved with sulfidic sediments, black shales, [[chert]]s and tholeiitic [[basalts]]. Komatiites were produced from a relatively wet [[Mantle (geology)|mantle]]. Evidence of this is from their association with [[felsic]]s, occurrences of komatiitic [[tuff]]s, [[niobium]] anomalies and by S- and H<sub>2</sub>O-borne rich mineralizations.

=== Textural features ===
[[File:CSIRO ScienceImage 1484 Komatiite Pyroxene Needles.jpg|thumb|[[Photomicrograph]] of a [[thin section]] of komatiite showing spinifex texture of pyroxene needle-like crystals]]
A common and distinctive texture is known as ''spinifex texture'' and consists of long [[Crystal habit|acicular]] phenocrysts of olivine (or [[pseudomorph]]s of alteration minerals after olivine) or pyroxene which give the rock a bladed appearance especially on a weathered surface. Spinifex texture is the result of rapid crystallization of highly magnesian liquid in the thermal gradient at the margin of the flow or [[Sill (geology)|sill]].

''Harrisite texture'', first described from [[intrusive rock]]s (not komatiites) at [[Harris Bay]] on the island of [[Rùm]] in [[Scotland]], is formed by nucleation of crystals on the floor of a [[magma chamber]].<ref>{{Cite journal|last1=O'Driscoll|first1=B.|last2=Donaldson|first2=C. H.|last3=Troll|first3=V. R.|last4=Jerram|first4=D. A.|last5=Emeleus|first5=C. H.|date=2006-11-13|title=An Origin for Harrisitic and Granular Olivine in the Rum Layered Suite, NW Scotland: a Crystal Size Distribution Study|journal=Journal of Petrology|volume=48|issue=2|pages=253–270|doi=10.1093/petrology/egl059|issn=0022-3530|doi-access=free}}</ref><ref>{{Cite journal|last1=Troll|first1=V R|last2=Mattsson|first2=T|last3=Upton|first3=B G J|last4=Emeleus|first4=C H|last5=Donaldson|first5=C H|last6=Meyer|first6=R|last7=Weis|first7=F|last8=Dahrén|first8=B|last9=Heimdal|first9=T H|date=2020-10-09|title=Fault-Controlled Magma Ascent Recorded in the Central Series of the Rum Layered Intrusion, NW Scotland|journal=Journal of Petrology|volume=61|issue=10|doi=10.1093/petrology/egaa093|issn=0022-3530|doi-access=free|hdl=10023/23208|hdl-access=free}}</ref> Harrisites are known to form megacrystal [[Aggregate (geology)|aggregate]]s of pyroxene and olivine up to 1 metre in length.<ref>{{Cite journal|last1=Emeleus|first1=C. H.|last2=Troll|first2=V. R.|date=August 2014|title=The Rum Igneous Centre, Scotland|journal=Mineralogical Magazine|language=en|volume=78|issue=4|pages=805–839|doi=10.1180/minmag.2014.078.4.04|bibcode=2014MinM...78..805E|issn=0026-461X|doi-access=free}}</ref> Harrisite texture is found in some very thick lava flows of komatiite, for example in the Norseman-Wiluna Greenstone Belt of Western Australia, in which crystallization of [[cumulate]]s has occurred.<ref name="Hill_et_al_1995">{{cite journal | title=The volcanology of komatiites as deduced from field relationships in the Norseman-Wiluna greenstone belt, Western Australia | first1=R.E.T. | last1=Hill | first2=S.J. | last2=Barnes |author-link2= Sarah-Jane Barnes|first3=M.J. | last3=Gole | first4=S.E. | last4=Dowling | journal=Lithos | year=1995 | volume=34 | issue=1–3 | pages=159–188 | doi=10.1016/0024-4937(95)90019-5| bibcode=1995Litho..34..159H }}</ref>  

[[File:KomatiiteA2.jpg|right|thumb|A2 facies dendritic feathery olivine crystals, drill hole WDD18, [[Widgiemooltha, Western Australia]]]]
[[File:KomatiiteA3.jpg|right|thumb|A3 facies bladed olivine spinifex, drill hole WDD18, Widgiemooltha Komatiite, Western Australia]]

=== Volcanology ===
{{Unreferenced section|date=November 2020}}
Komatiite [[volcano]] morphology is interpreted to have the general form and structure of a [[shield volcano]], typical of most large [[basalt]] edifices, as the magmatic event which forms komatiites erupts less magnesian materials.

However, the initial flux of the most magnesian magmas is interpreted to form a channelised flow facie, which is envisioned as a fissure vent releasing highly fluid komatiitic lava onto the surface. This then flows outwards from the vent fissure, concentrating into topographical lows, and forming channel environments composed of high MgO olivine [[Cumulate rock|adcumulate]] flanked by a 'sheeted flow facies'  aprons of lower MgO olivine and pyroxene thin-flow spinifex sheets.

The typical komatiite lava flow has six stratigraphically related elements;
* A1 – pillowed and variolitic chilled flow top, often grading and transitional with sediment
* A2 – Zone of quickly chilled, feathery acicular olivine-clinopyroxene-glass representing a [[chilled margin]] on the top of the flow unit
* A3 – Olivine spinifex sequence composed of sheaf and book-like olivine spinifex, representing a downward-growing crystal accumulation on the flow top
* B1 – Olivine mesocumulate to orthocumulate, representing a harrisite grown in flowing liquid melt
* B2 – Olivine adcumulate composed of >93% interlocking equant olivine crystals
* B3 – Lower chill margin composed of olivine adcumulate to mesocumulate, with finer grain size.
Individual flow units may not be entirely preserved, as subsequent flow units may thermally erode the A zone spinifex flows. In the distal thin flow facies, B zones are poorly developed to absent, as not enough through-flowing liquid existed to grow the adcumulate.

The channel and sheeted flows are then covered by high-magnesian basalts and tholeiitic basalts as the volcanic event evolves to less magnesian compositions. The subsequent magmatism, being higher silica melts, tends to form a more typical shield volcano architecture.

=== Intrusive komatiites ===
{{Unreferenced section|date=November 2020}}
Komatiite magma is extremely dense and unlikely to reach the surface, being more likely to pool lower within the crust. Modern (post-2004) interpretations of some of the larger olivine adcumulate bodies in the [[Yilgarn craton]] have revealed that the majority of komatiite olivine adcumulate occurrences are likely to be [[subvolcanic rock|subvolcanic]] to [[Intrusive rock|intrusive]] in nature.

This is recognised at the [[Mount Keith Mine|Mt Keith]] [[nickel]] deposit where wall-rock intrusive textures and [[xenolith]]s of [[felsic]] country rocks have been recognised within the low-strain contacts.<ref>Rosengren, N. M., Beresford, S. W., Grguric, B. A., & Cas, R.A.F. 2005. An intrusive origin for the komatiitic dunite-hosted Mount Keith disseminated nickel sulfide deposit, Western Australia. Economic Geology, 100(1), 149–156. https://doi.org/10.2113/100.1.0149</ref> The previous interpretations of these large komatiite bodies was that they were "super channels" or reactivated channels, which grew to over 500 m in stratigraphic thickness during prolonged volcanism.

These intrusions are considered to be ''channelised sills'', formed by injection of komatiitic magma into the stratigraphy, and inflation of the magma chamber. Economic nickel-mineralised olivine adcumulate bodies may represent a form of sill-like conduit, where magma pools in a staging chamber before erupting onto the surface.

== Economic importance ==
{{Unreferenced section|date=November 2020}}
The economic importance of komatiite was first widely recognised in the early 1960s with the discovery of [[Kambalda type komatiitic nickel ore deposits|massive nickel sulfide mineralisation]] at [[Kambalda, Western Australia]]. Komatiite-hosted nickel-copper sulfide mineralisation today accounts for about 14% of the world's [[nickel]] production, mostly from Australia, Canada and South Africa.

Komatiites are associated with nickel and [[gold]] deposits in Australia, Canada, South Africa and most recently in the [[Guiana Shield|Guiana shield]] of South America.

== See also ==
* {{annotated link|List of rock textures}}
* {{annotated link|List of rock types}}
* {{annotated link|Igneous rock}}
* {{annotated link|Rock microstructure}}
* {{annotated link|Kambalda type komatiitic nickel ore deposits|Komatiitic Ni-Cu-PGE mineralisation}}
* {{annotated link|Ultramafic rock}}
* {{annotated link|Cumulate rock}}

== References ==
{{reflist}}

==Bibliography==
* Hess, P. C. (1989), ''Origins of Igneous Rocks'', President and Fellows of Harvard College (pp.&nbsp;276–285), {{ISBN|0-674-64481-6}}.
* Hill R.E.T, Barnes S.J., Gole M.J. and Dowling S.E. (1990), ''Physical volcanology of komatiites; A field guide to the komatiites of the Norseman-Wiluna Greenstone Belt, Eastern Goldfields Province, Yilgarn Block, Western Australia.'', Geological Society of Australia. {{ISBN|0-909869-55-3}}
* Blatt, Harvey and Robert Tracy (1996), ''Petrology'', 2nd ed., Freeman (pp.&nbsp;196–7), {{ISBN|0-7167-2438-3}}.
* S. A. Svetov, A. I. Svetova, and H. Huhma, 1999, ''Geochemistry of the Komatiite–Tholeiite Rock Association in the Vedlozero–Segozero Archean Greenstone Belt, Central Karelia'', Geochemistry International, Vol. 39, Suppl. 1, 2001, pp. S24–S38. [https://web.archive.org/web/20040724032703/http://geoserv.karelia.ru/rus/htm_files/Personal/Svetov%20S_A/GeoChemS1_01SvetovLO.pdf PDF] accessed 7-25-2005
* Vernon R.H., 2004, ''A Practical Guide to Rock Microstructure'', (pp.&nbsp;43–69, 150–152) Cambridge University Press. {{ISBN|0-521-81443-X}}
* Arndt, N.T., and Nisbet, E.G. (1982), ''Komatiites''. Unwin Hyman, {{ISBN|0-04-552019-4}}. Hardcover.
* Arndt, N.T., and Lesher, C.M. (2005), Komatiites, in Selley, RC, Cocks, L.R.M., Plimer, I.R. (Editors), ''Encyclopedia of Geology'' 3, Elsevier, New York, pp.&nbsp;260–267
* Faure, F., Arndt, N.T. Libourel, G. (2006), Formation of spinifex texture in komatiite: An experimental study. J. Petrol 47, 1591–1610.
* Arndt, N.T., Lesher, C.M. and Barnes, S.J. (2008), ''Komatiite'', Cambridge University Press, Cambridge, 488 pp., {{ISBN|978-0521874748}}.

== External links ==
* [http://www.geology.sdsu.edu/how_volcanoes_work/Unusual%20lava.html Unusual lava types] {{Webarchive|url=https://web.archive.org/web/20171023185741/http://www.geology.sdsu.edu/how_volcanoes_work/Unusual%20lava.html |date=2017-10-23 }} accessed 7-25-2005
* [https://arxiv.org/abs/physics/0512118 Komatiites and astrobiology]
* [http://www.mantleplumes.org/Komatiites.html Komatiites and the Plume Debate]
* [http://www.xs4all.nl/~carlkop/iofire.html Volcanic fireworks on Io]
* [http://christian.nicollet.free.fr/page/Canada/komatiites.html Photos of Abitibi komatiite, Canada] (with text in French) retrieved 2009-05-17

{{Igneous rocks}}
{{Rock type}}
{{Volcanoes}}

[[Category:Ultramafic rocks]]
[[Category:Volcanology]]
[[Category:Igneous petrology]]
[[Category:Metamorphic rocks]]
[[Category:Volcanic rocks]]
[[Category:Subvolcanic rocks]]