Amy and her brother Sam are finding out about rocks. They have come back from holiday with several different kinds of rocks and they're having fun trying to sort them out.
"How shall we sort them, Amy?" Sam wanted to know.
"How about seeing if they're hard or soft?" suggested Amy.
"But aren't all rocks hard - isn't it going to hurt if I drop one on my toe?" asked Sam.
"Well, they might be heavy, but not all of them are hard. Some wear away quite easily." Amy told Sam.
Let's see how their rock investigation turns out.