If your Scout is working on a geology badge, he might need use a mineral hardness scale such as the Mohs’s Hardness Scale Scratch Test.
This tests gives scientists a concrete way to compare the hardness of different minerals. The hardness is measured by scratching other minerals with the mineral in question. Then the rock is ranked against the other substances based on which ones it scratched or did not scratch.
For example, if you can make a scratch on an item with a common nail, but not with a penny, you know it falls somewhere between 3 and 5 on the scale.