Radical 石
14 strokes
stone 石 (115a) + jet black 兹 (794b) = magnet 磁
磁带 (429) cídài magnetic (audio) tape

The children had each brought a jet black stone from the beach, and they wanted to make them into fridge magnet s. / The fairy tapped the stones with a staccato tap of her wand to render them magnetic.