Why is diamond hard?

It all comes down to how its carbon atoms are arranged. In a diamond, every single carbon atom is tightly linked to four of its neighbours. These connections are incredibly strong covalent bonds. This creates a rigid, three-dimensional lattice structure that's extremely difficult to break apart. Think of it as a perfect, tightly-knit framework. To scratch a diamond, you would need to break these powerful atomic bonds. Because it takes so much energy to do that, diamond ends up being the hardest natural substance we know. It’s a beautiful example of strength in structure.