Magnetite is the most common mineral that is strongly magnetic. Magnetite, like hematite, is an iron oxide, but with a slightly different chemical formula - Fe3O4. Magnetite has a metallic luster, a dark gray to black color, a blackish-colored streak, is fairly hard (H=6), has no cleavage, and is moderately heavy for its size.
Until the 1960s, magnetite was the most important iron ore mineral (“hard iron ore”). Magnetite tends to have high levels of impurities, however. Physical processing of hematite (Fe2O3) (“soft iron ore”), produces higher-quality pellets for the iron smelters.
Magnetite (4.6 cm across)