Is diamond the hardest substance on Earth?

Yes, diamond is the hardest naturally occurring substance on Earth. It is a 10 on the Mohs scale of mineral hardness, indicating the material’s supreme resistance to being scratched. Diamond’s hardness is a result of its atomic structure, where each carbon atom (diamond is made entirely of carbon) is bonded to four equally spaced neighbors in a dense tightly bonded structure. The extreme hardness of diamond makes it invaluable in industrial applications, particularly for cutting, drilling, or as an abrasive. (see also How Are Diamonds Made?)