noun
: the red or black crystalline sesquioxide of iron Fe 2 O 3 that is found in nature both as hematite and as hydrated forms (as rust and limonite) and is also obtained synthetically (as by calcining ferrous sulfate or hydrated ferric oxide) and that is used chiefly as a pigment and polishing material and in the removal of hydrogen sulfide from gases — called also iron(III) oxide ; compare iron oxide a, iron red , rouge 2