High School Earth Science/Identification of Minerals - Hardness. 1  Hardness is a mineral's ability to resist being scratched. Minerals that are not easily scratched are hard. 2  As you can see, diamond is a 10 on Mohs Scale. Diamond is the hardest mineral, which means that no other mineral can scratch a diamond. Quartz is a 7, so it can be scratched by topaz, corundum, and diamond. Quartz will scratch minerals, such as fluorite, that have a lower number on the scale. Suppose you tested a piece of pure gold for hardness. Calcite would scratch the gold, but gypsum would not because gypsum is a 2 and calcite is a 3.