Three tests that cost almost nothing and settle most arguments: streak (hematite versus magnetite in one stroke), a pocket magnet, and learning to feel specific gravity by hand with galena as the anchor. Each test comes with a five-minute classroom demonstration script.
The classroom set-piece
Hand students one hematite and one magnetite — both black, both heavy, both confidently misidentified. One stroke each on a streak plate (red-brown versus black) and one pass with a magnet settles it in under a minute, and nobody forgets the lesson. The two identification sheets carry the full property tables.