Magnetite (iron oxide) is the most magnetic naturally occurring mineral — a small magnet will cling to it directly. Combine that with a black streak and octahedral crystal habit to separate it cleanly from hematite (reddish-brown streak, at most weakly magnetic) and ilmenite. Common in igneous and metamorphic rocks and as black sand in streams.
Field identification workflow
- Bring the magnet to the rock: magnetite grabs it. No other common black mineral does this with conviction.
- Streak black — this cleanly separates it from hematite's red-brown, even when the hand specimens look like twins.
- Look for octahedra: tiny pyramids-on-pyramids in schist or beach sand are classic.
- Pan a stream: the black sand that follows your magnet around the pan is magnetite, and a good teaching prop costs nothing.