Diamond ranks 10 on the Mohs hardness scale, making it the hardest naturally occurring mineral.
Its extreme hardness comes from carbon atoms linked in a rigid three-dimensional crystal lattice. Each carbon atom bonds strongly to four neighbors, producing a structure that resists scratching.
Diamond is not the same as graphite, even though both are made of carbon. Graphite has layered bonds and is soft, which shows how crystal structure can dramatically change a material’s properties.
Mohs hardness measures resistance to scratching, not toughness or resistance to breaking. Diamond can still chip or fracture, despite being harder than every other mineral on the scale.