What is the hardest natural substance on Earth?

Diamond is recognized as the hardest natural substance on Earth due to its unique crystalline structure and the strong covalent bonding between its carbon atoms. Each carbon atom in a diamond is bonded to four other carbon atoms in a three-dimensional arrangement, creating a very strong lattice. This structure grants diamonds exceptional hardness, making them capable of scratching nearly all other materials.

In contrast, gold and iron, while they are strong metals, do not possess the same level of hardness attributed to diamonds. Gold is known for its malleability and ductility, making it less suitable for scratching other substances. Iron also has strength but is much softer compared to diamonds. Emeralds, although beautiful and valuable, are composed of beryl which contains some hardness but still does not approach that of diamonds, ranking lower on the Mohs scale of mineral hardness. Thus, the distinctive structural properties of diamond solidify its status as the hardest natural substance on Earth.