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]