pyroxene , A group of important rock-forming silicate minerals of variable composition, among which calcium-, magnesium-, and iron-rich varieties predominate. Common pyroxenes belong to either the low-calcium enstatite-(ortho)ferrosilite series, (Mg,Fe)SiO3, or the high-calcium diopside-hedenbergite series, Ca(Mg,Fe)Si2O6. Rare pyroxenes include jadeite, aegirine, and johannsenite. See also enstatite.