Diamonds are renowned not only for their beauty but also for being the hardest natural material on Earth. On the Mohs scale of mineral hardness, diamonds rank at a perfect 10, which places them far above most other gemstones and minerals.

Why Are Diamonds So Hard?
The extraordinary hardness of diamond is due to its unique crystal structure:
Each carbon atom is tetrahedrally bonded to four other carbon atoms. These bonds form a three-dimensional lattice of covalent bonds, which are among the strongest in nature. This ultra-strong atomic structure makes diamond exceptionally resistant to scratching — no other natural substance can scratch a diamond except another diamond.

Hardness vs. Toughness
It’s important to distinguish between hardness and toughness:
Hardness refers to resistance to scratching. Toughness refers to resistance to breaking or chipping. While diamonds are incredibly hard, they are not the toughest material. Due to their cleavage planes, diamonds can chip or fracture if struck sharply at the right angle. 

Practical Implications
Diamond’s hardness makes it ideal for industrial cutting, drilling, and grinding tools. In jewelry, it helps ensure that the stone remains free of scratches over years of wear.