Magnetite

As you  might expect, magnetite is magnetic.

Physical Properties
Chemical formula Fe3O4
Class Oxide
Crystal system Cubic
Habit Typically octahedral
May display contact or lamellar twins
Massive or granular aggregates
Disseminated as fine grains
Color Black
Hardness 6
Specific gravity 5.2
Cleavage None
Fracture Subconchoidal
Luster Metallic
Transparency Opaque
Streak Black
Special properties Magnetic
after Perkins, 375

Magnetite in Hand Sample

Magnetite with fayalite

Euhedral magnetite crystals in a muscovite magnetite schist

Further Reading

Magnetite at webmineral.com

Magnetite at mindat.org