Aegirine is a member of the clino
pyroxene group of
inosilicates. Aegirine is the sodium endmember of the aegirine-
augite series. Aegirine has the chemical formula
NaFeSi2O6 in which the iron is present as Fe
3+. In the aegirine-augite series the sodium is variably replaced by calcium with iron(II) and magnesium replacing the iron(III) to balance the charge. Aluminium also substitutes for the iron(III). It is also known as
acmite, which is a fibrous, green-colored variety.