The Mohs Hardness Scale ranks the order of hardness of minerals and some common objects. For example, your fingernail can scratch the minerals talc and gypsum, with a hardness of 2 or lower. A copper penny can scratch calcite, gypsum, and talc.

A common misunderstanding of how to identify a diamond is that it will scratch glass. While this is true, other minerals can scratch glass, too, as long as they have a hardness >6.