The Collaborative International Dictionary
Martite
Martite \Mar"tite\, n. [L. Mars, Martis, the god Mars, the alchemical name of iron.] (Min.) Iron sesquioxide in isometric form, probably a pseudomorph after magnetite.
Wiktionary
martite
n. (context geology mineralogy English) A variety of hematite that is pseudomorphic after magnetite crystals.