What contributes to a diamond's supreme hardness and durability?

A diamond's supreme hardness and durability primarily stem from the specific conditions under which it formed deep within the Earth's mantle. Diamonds are created under high-pressure and high-temperature conditions, allowing carbon atoms to bond in a precise crystal lattice structure known as a diamond cubic. This unique arrangement of atoms gives diamonds their renowned hardness, making them the hardest known natural material.

While factors such as the cut and polish contribute to the appearance and brilliance of a diamond, they do not affect its inherent hardness or durability that originate from its geological formation. The size of the diamond can influence value and aesthetic appeal, but it does not directly correlate with the hardness itself. Similarly, market demand may affect pricing and sales but has no impact on the physical properties of the diamond. Thus, the correct answer highlights the importance of the formation conditions in determining a diamond's exceptional qualities.