It depends on how strong a magnet you are using, the weight of the stone, what iron mineral the rock is, etc. Magnetite maybe, hematite maybe not. Check em out online.
i use a rare earth magnet on a 2in x 36 pvc to pickup trash when i go coin hunting,so iam hoping to use it for the rocks this weekend looking for gold were there are allot of iron rocks.i forgot what pounds of pull it is buts its allot.
thanks brad