What is the hardest natural substance on Earth?

The hardest natural substance on Earth is diamond. Diamonds are formed deep within the Earth's mantle under extreme pressure and temperature conditions. Their unique crystal structure, composed of carbon atoms arranged in a three-dimensional lattice, contributes to their exceptional hardness. This hardness is measured on the Mohs scale, where diamond ranks at the top with a value of 10, making it ideal for cutting and grinding tools.

Gold, iron, and granite lack the same level of hardness as diamond. Gold is a relatively soft metal used primarily for jewelry and electronics. Iron, while strong, is not as hard as diamond and is more prone to rust and oxidation. Granite, being an igneous rock, is harder than many other materials but still does not match the hardness of diamond due to its composition and the minerals it contains. Thus, the unique properties of diamond make it the hardest known natural material, surpassing all other candidates listed.