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This article was most recently revised and updated by John P. Rafferty. Orthopyroxene, any of a series of common silicate minerals in the pyroxene family. Orthopyroxenes typically occur as fibrous or lamellar (thin-plated) green masses in igneous and metamorphic rocks and in meteorites.
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Orthopyroxene high in Mg is common in gabbro and peridotite groups. Fe-rich orthopyroxene is typically found in diorite, syenite and granite. With Ca-clinopyroxene, plagioclase and olivine in mafic and ultramafic igneous rocks. Associated Minerals. Feldspars, clinopyroxene, garnet, biotite and hornblende. Editors.
Orthopyroxenes are relatively widespread as a primary mineral in gabbroic and ultramafic rocks where they form with augite, olivine and plagioclase. Orthopyroxene may occur in high grade metamorphic rocks. It is essential in the granitic gneisses called charnockites, and may be found in pyroxene granulites and metamorphosed iron formations.
Pyroxenes are the most common single-chain silicate minerals. (The only other important group of single-chain silicates, the pyroxenoids, are much less common.) Their structure consists of parallel chains of negatively-charged silica tetrahedra bonded together by metal cations. In other words, each silicon ion in a pyroxene crystal is ...
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Orthopyroxene. Orthopyroxene Occurrence. Orthopyroxene is common in mafic igneous rocks, ingcluding gabbro, basalt and norite, commonly associated with plagioclase and clinopyroxene . It is also found in some high grade metamorphic rocks. The term "hypersthene" is often used as a synonym for orthopyroxene.
Orthopyroxenes and clinopyroxenes are highly magnesian with an Mg number ranging 0.89 to 0.96 (geometric mean: 0.92; standard deviation: 0.02) and 0.89 to 0.98 (geometric mean: 0.93; standard deviation: 0.02), respectively. Orthopyroxenes and clinopyroxenes have a high content of Al 2 O 3, at 3.13–5.30 wt.% and 1.79–6.45 wt.%, respectively.
Dec 16, 2022 · Natural pyroxenes fall into two main series, distinguished by slightly different atomic arrangements and different crystal shapes: the orthopyroxene series (Opx) and the clinopyroxene series (Cpx). Orthopyroxenes, predominantly solid solutions of the end members ferrosilite and enstatite, have the general formula (Mg,Fe) 2 Si 2 O 6 .
