The six strongest materials on Earth are harder than diamonds | by Ethan Siegel | Starts With A Bang! | May, 2025

For millennia, diamonds were the hardest known material, but they only rank at #7 on the current list. Can you guess which material is #1?

Carbon is one of the most fascinating elements in all of nature, with chemical and physical properties unlike any other element. With just six protons in its nucleus, it’s the lightest abundant element capable of forming a slew of complex bonds. All known forms of life are carbon-based, as its atomic properties enable it to link with up to four other atoms at a time, from the simplest such structure possible (methane) to incredibly rich molecules containing trillions of atoms or more. The possible geometries of those bonds also enable carbon to self-assemble, particularly under high pressures, into a stable crystal lattice.

If the conditions are just right, with impurity-free carbon and the needed pressures and temperatures, carbon atoms can form a solid, ultra-hard structure known as a diamond. Although diamonds are commonly known as “the hardest material in the world,” there are actually six materials that are harder. Diamonds are still one of the hardest naturally occurring (and, perhaps surprisingly, quite abundant) materials on Earth, and yet these six materials all have diamonds…