You need a pair of safety glasses, a piece of card to catch the sand, and two soft rounded stones to make the sand. Chalk or soft sandstone are best. If you do not have these, use two pieces of bathroom pumice stone or two sticks of blackboard chalk instead. Knock one stone against the other with short, glancing blows above the card. Look to see the kind of material that falls on to the card. What has it done to the stones?
