For gemstones, the scientific definition of hardness refers only to a gemstone’s ability to resist scratching. Diamonds are the hardest natural material in the world and have a Mohs hardness scale of 10. The Mohs scale ranks materials on their hardness and grades them using numbers from 1-10. For metals, the Mohs scale indicates which other metals can scratch it. Gold, for example, has a hardness scale of 2.53, which is lower than most other metals such as silver, copper, bronze and others.
