{{Short description|Igneous rocks which have a deficiency of aluminium}}
thumb | Chart illustrating the meaning of peralkaline, metaluminous, peraluminous and subaluminous '''Peralkaline rocks''' include those igneous rocks which have a deficiency of aluminium such that sodium and potassium are in excess of that needed for feldspar. The presence of aegerine (sodium pyroxene) and riebeckite (sodium amphibole) are indicative of peralkaline conditions. Examples are the peralkaline rhyolites, comendite and pantellerite,<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=9780521880060 |pages=143–146 |edition=2nd}}</ref> with comendite being the more felsic (silica-rich) rock.<ref>{{cite book |last1=McBirney |first1=Alexander R. |title=Igneous petrology |date=1984 |publisher=Freeman, Cooper |location=San Francisco, Calif. |isbn=0198578105 |page=502}}</ref> Another example is the peralkaline granite that forms the islet of Rockall in the North Atlantic Ocean.<ref name="DSutherland1982">{{cite book | title=Igneous Rocks of the British Isles | publisher=John Wiley and Sons | author=Sutherland, D. S. (editor) | year=1982 | location=Chichester | page=413 | isbn=978-0-471-27810-8}}</ref>
Peralkaline rocks are indicative of continental rift-related volcanicity (e.g. the peralkaline rhyolites of the East African Rift in central Kenya) as well as continental and oceanic hotspot volcanicity (e.g. the peralkaline rhyolites of the Glass House Mountains in eastern Australia and the Canary Islands in the Atlantic Ocean).<ref name="Scaillet-Macdonald2003">{{cite journal | title=Experimental Constraints on the Relationships between Peralkaline Rhyolites of the Kenya Rift Valley | first1=Bruno | last1=Scaillet | first2=Ray | last2=Macdonald | journal=Journal of Petrology | year=2003 | volume=44 | issue=10 | pages=1867–1894 | doi=10.1093/petrology/egg062| bibcode=2003JPet...44.1867S | doi-access=free }}</ref><ref name="GE">{{cite journal|last1=Shao|first1=Fengli|last2=Niu|first2=Yaoling|last3=Regelous|first3=Marcel|last4=Zhu|first4=Di-Cheng|title=Petrogenesis of peralkaline rhyolites in an intra-plate setting: Glass House Mountains, southeast Queensland, Australia|publisher=Elsevier|journal=Lithos|year=2015|volume=216|pages=196–210|doi=10.1016/j.lithos.2014.12.015|bibcode=2015Litho.216..196S|issn=0024-4937}}</ref><ref>{{cite journal|last1=Troll|first1=Valentin R.|last2=Schmincke|first2=Hans-Ulrich|title=Magma Mixing and Crustal Recycling Recorded in Ternary Feldspar from Compositionally Zoned Peralkaline 'A', Gran Canaria, Canary Islands|publisher=Oxford Academic Journals|journal=Journal of Petrology|year=2002|page=246|volume=43|issue=2|doi=10.1093/petrology/43.2.243|issn=0022-3530|doi-access=free}}</ref> Peralkaline rocks related to subduction zone volcanicity have also been reported (e.g. Sardinia in Italy).<ref name="GE"/> Peralkaline magmas likely form when fractional crystallization removes a high proportion of plagioclase relative to mafic minerals.{{sfn|McBirney|1984|pp=396-397}}
==See also== * Agpaitic rock * Metaluminous rock * Peraluminous rock
==References== {{reflist}}
Category:Igneous rocks Category:Volcanology Category:Igneous petrology
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