What is the hardest rock?

The hardest rock is diamond, which is well-known for its exceptional hardness. In fact, diamond ranks at the top of the Mohs scale of mineral hardness, scoring a perfect 10. This scale is used to measure the scratch resistance of various minerals. The atomic structure of diamond, where carbon atoms are arranged in a tetrahedral lattice, contributes to its strength and durability, making it ideal for cutting tools and jewelry.

While ruby is also a hard gemstone, it is not as hard as diamond; it scores a 9 on the Mohs scale. Granite and basalt are types of igneous rock that are much softer than diamond; granite typically falls around a 6-7 when tested for hardness, while basalt is also in a similar range. Therefore, diamond stands out as the hardest known naturally occurring material, which is why it is the correct answer.