Pyroxene: Difference between revisions

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[[File:Diopside-172005.jpg|thumb|Pyroxene ([[diopside]]) crystals from [[Afghanistan]]]]The '''pyroxenes''' (commonly abbreviated to ''Px'') are a group of important rock-forming [[Silicate minerals#Inosilicates|inosilicate]] [[mineral]]s found in many [[Igneous rock|igneous]] and [[metamorphic rock|metamorphic]] [[rock (geology)|rocks]]. Pyroxenes have the general formula {{chem2|XY(Si,Al)2O6}}, where X represents [[calcium]] (Ca), [[sodium]] (Na), [[iron]] (Fe II) or [[magnesium]] (Mg) and more rarely [[zinc]], [[manganese]] or [[lithium]], and Y represents ions of smaller size, such as [[chromium]] (Cr), [[aluminium]] (Al), iron (Fe III), [[magnesium]] (Mg), [[cobalt]] (Co), [[manganese]] (Mn), [[scandium]] (Sc), [[titanium]] (Ti), [[vanadium]] (V) or even iron (Fe II). Although aluminium substitutes extensively for silicon in silicates such as [[feldspar]]s and [[amphibole]]s, the substitution occurs only to a limited extent in most pyroxenes. They share a common structure consisting of single chains of silica [[tetrahedra]]. Pyroxenes that crystallize in the [[monoclinic]] system are known as '''clinopyroxenes''' and those that crystallize in the [[orthorhombic]] system are known as '''orthopyroxenes'''.

The name ''pyroxene'' is derived from the Ancient Greek words for ''fire'' ({{transl|grc|pyr}} {{wikt-lang|grc|πυρ}}) and ''stranger'' ({{transl|grc|ksénos}} {{wikt-lang|grc|ξένος}}). Pyroxenes were so named because of their presence in volcanic lavas, where they are sometimes found as crystals embedded in volcanic [[glass]]; it was assumed they were impurities in the glass, hence the name "firemeaning 'fire-strangers"'. However, they are simply early-forming minerals that crystallized before the lava erupted.

The [[upper mantle (Earth)|upper mantle]] of Earth is composed mainly of [[olivine]] and pyroxene minerals. Pyroxene and [[feldspar]] are the major minerals in [[basalt]], [[andesite]], and [[gabbro]] rocks.<ref>{{Cite journal|last=Deegan|first=Frances M.|last2=Whitehouse|first2=Martin J.|last3=Troll|first3=Valentin R.|last4=Budd|first4=David A.|last5=Harris|first5=Chris|last6=Geiger|first6=Harri|last7=Hålenius|first7=Ulf|date=2016-12-30|title=Pyroxene standards for SIMS oxygen isotope analysis and their application to Merapi volcano, Sunda arc, Indonesia|url=http://www.sciencedirect.com/science/article/pii/S0009254116305496|journal=Chemical Geology|language=en|volume=447|pages=1–10|doi=10.1016/j.chemgeo.2016.10.018|issn=0009-2541}}</ref><ref>{{Cite journal|last=O’Driscoll|first=Brian|last2=Stevenson|first2=Carl T. E.|last3=Troll|first3=Valentin R.|date=2008-05-15|title=Mineral Lamination Development in Layered Gabbros of the British Palaeogene Igneous Province: A Combined Anisotropy of Magnetic Susceptibility, Quantitative Textural and Mineral Chemistry Study|url=https://doi.org/10.1093/petrology/egn022|journal=Journal of Petrology|volume=49|issue=6|pages=1187–1221|doi=10.1093/petrology/egn022|issn=1460-2415}}</ref>

==Chemistry and nomenclature of the pyroxenes==