Pyroxene (Gr. , fire, and , a stranger), a mineral species of Dana's augite section of the silicates, comprising numerous varieties. That to which the name was first applied, though found in the so-called igneous rocks, was supposed not to occur in modern lavas; whence the name. The species is interesting for its many varieties, which differ in physical characters and chemical constituents, and consequently have been separated by different mineralogists among several species. They were first brought together under the head of pyroxene by Haüy, who recognized the identity of the crystalline form common to them all; and though for a time the relationship among them was not admitted by chemists, it was at last found that the differences in their composition resulted from the substitution of one isomorphous element for another, and that one general formula might be used to express the combination of silicic acid with one or more of the following bases (one replaced by another in any proportions), viz.: lime, magnesia, protoxide of iron, or manganese, and sometimes soda. Alumina may also enter into the composition, replacing it may be a portion of silicic acid, without essentially changing the crystallization.
Among the varieties comprised in this species are the augites, coccolite, diop-side, sahlite, jeffersonite, and many others.