Pyroxene mineral, sodium and iron silicate (NaFe+3SiO), commonly found in alkaline igneous rocks, particularly in syenites (composed of an alkali feldspar and a ferromagnesian mineral) and syenite pegmatites. It also occurs in schists. Aegirine is generally dark green to greenish black.
Aegirine crystals from Magnet Cove, Arkansas—Courtesy of the Field Museum of Natural History, Chicago; photograph, John H. Gerard
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