Pyroxene mineral, sodium and iron silicate (NaFe +3 Si 2 O 6 ), 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
By courtesy of the Field Museum of Natural History, Chicago; photograph, John H. Gerard