From The Collaborative International Dictionary of English v.0.48 :
Magnetite \Mag"net*ite\, n. (Min.) An oxide of iron ({Fe3O4) occurring in isometric crystals, also massive, of a black color and metallic luster. It is readily attracted by a magnet and sometimes possesses polarity, being then called loadstone. It is an important iron ore. Called also magnetic iron. [1913 Webster]From WordNet (r) 3.0 (2006) :
magnetite n 1: an oxide of iron that is strongly attracted by magnets [syn: magnetite, magnetic iron-ore]