The World Around Us

Chemicals in the Natural World

Why is diamond so hard?

Pure diamond is a crystalline form of only carbon atoms. The crystal lattice is three-dimensional, and all carbon atoms are attached to four other carbon atoms in a perfect tetrahedral geometry. Because the lattice repeats in all three dimensions, there is no easy way to distort the structure, making it a very hard material. The structure of graphite, for comparison, is many stacked-up layers of carbon atoms. These two-dimensional sheets can “slide” relative to one another, making graphite relatively soft in comparison to diamond.


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