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Orthorhombic system
- The orthopyroxene series crystallizes in the orthorhombic system (three crystallographic axes unequal in length and at right angles to each other).
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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 .
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' (πυρ, pur) and 'stranger' (ξένος, xénos).
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.
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.
The orthopyroxene series crystallizes in the orthorhombic system (three crystallographic axes unequal in length and at right angles to each other). An analogue crystallizing in the monoclinic system (three crystallographic axes unequal in length with one oblique intersection), the clinoenstatite–clinoferrosilite series is found largely in ...
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structure. Figure 1: Single pyroxene chain, (SiO 3) n, in three projections: (A) along the c axis direction, (B) on (100), a plane that intersects the a axis and is parallel to the b and c axes, and (C) along the b axis direction. The pyroxene group includes minerals that form in both the orthorhombic and monoclinic crystal systems.
In the synthetic system MgO-SiO 2 -H 2 O, enstatite crystallizes at temperatures above 650°C at water vapor pressures greater than 350 bars and is stable in the presence of water vapor below about 850°C. Various approaches have been made to the development of a pyroxene geothermometer (see Thermometry, Geologic ).
