Diamonds may still be a girl’s best friend, but they can no longer claim to be the hardest substance on earth. As of 2005, that distinction is now claimed by buckyballs. Readers of Commonplace already know that buckyballs (more properly known as buckminsterfullerene) are the among most expensive substances in the world. This scientifically-engineered substance already outshines the diamond as far as the price tag ($167 million per gram). Now we know it has also supplanted the diamond’s claim to the hardest known substance.
When scientists at Germany’s Bayreuth University created the new substance, they started with the same building blocks as a diamond: carbon atoms. Whereas the carbon atoms in a diamond are stacked like a pyramid, each buckyball is made of 60 carbon atoms, arranged like a soccer ball.
The result of this atomic manipulation made the substance incredibly hard. Friedrich Mohs (1773–1839) devised the Mohs hardness scale in 1812. It determines hardness on the basis of which substance is able to scratch another. It starts at the softest end with talc (MH1). Lead is fairly soft at MH1 ½; fingernails are graded MH2 ½ (as hard as gold); in the middle are glass and knife blades at MH5 ½. Ordinary sandpaper (which is made of corundum) is MH9, and right at the top end is diamond at MH10. Buckyballs can scratch diamonds, so they are literally off the scale.
Not to be outdone, buckyballs have also taken the title for the stiffest and densest substances currently known.
Stiffness is determined by the amount of force that must be applied equally on all sides to make the material shrink in volume. Its basic unit is the pascal, after Blaise Pascal (1623–62). Buckyballs’ stiffness rating is 491 gigapascals (GPa), compared to 442 GPa for a diamond and 180 GPa for iron.
Density is measured by how tightly packed are the material’s molecules. Buckyballs are 0.3 percent denser than diamonds.
With all that going for it, don’t expect buckyballs to be the choice for engagement rings any time soon. While the substance may outperform diamonds in the categories of price, hardness, stiffness, and density, they have the appearance of asphalt and are unlikely to catch the eye of anyone other than a physicist.