Which mineral is the most common natural magnetic mineral?

Magnetite is the most common natural magnetic mineral.

Magnetite is an iron oxide with the formula Fe₃O₄. It is usually black, has a metallic to dull luster, and is strongly magnetic. Naturally magnetized pieces are called lodestones and were important in the early development of the magnetic compass.

Magnetite belongs to the spinel group and contains iron in two oxidation states. Its magnetic behavior is linked to the arrangement of those iron ions in its crystal structure. Magnetite commonly occurs in igneous, metamorphic, and sedimentary rocks, and it can be concentrated in black-sand deposits because of its high density.

Magnetite is also an important iron ore. It can oxidize to hematite or other iron oxides near Earth’s surface. Although hematite may look similar, ordinary hematite is weakly magnetic or nonmagnetic, so appearance alone is not a reliable identification test.