magnetite

Bring a magnet. Magnetite is the part of the black sand a magnet lifts out: drag one through dry sand at the waterline and it comes up bearded with black grains. The rest of that black sand is mostly ilmenite, garnet, amphibole and pyroxene. A weak magnet leaves those lying there, though a strong neodymium one will start pulling ilmenite too. A pebble of it is black, noticeably heavy, and the magnet sticks.

That one test settles the whole argument. Hematite streaks rust-red and mostly ignores the magnet; plain basalt is lighter in the hand and does nothing at all.