pyroxene quadrilateral
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The pyroxene quadrilateral is a compositional diagram used to classify pyroxenes, a group of rock-forming silicate minerals. It represents the chemical system of calcium, magnesium, and iron silicates that form pyroxenes. The diagram's vertices correspond to ideal end-member compositions: CaSiO₃ (wollastonite, a pyroxenoid), MgSiO₃ (enstatite), and FeSiO₃ (ferrosilite).1
Pyroxenes crystallize in both orthorhombic and monoclinic systems. Their structure features chains of silicon-oxygen tetrahedrons. They are chemically analogous to amphiboles but lack essential hydroxyls in their structure. Pyroxenes are common in high-temperature igneous and metamorphic rocks.21
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