Ultrahard fullerite (C₆₀) is a form of carbon found to be harder than diamond, and which can be used to create even harder materials, such as aggregated diamond nanorods.

Specifically, it is a unique version of fullerene with three-dimensional polymer bonds. This should not be confused with P-SWNT fullerite, even though that material is also a polymerized version of fullerene. It has been shown 1 2 that ultrahard fullerite when testing diamond hardness with a scanning force microscope of specific construction can scratch diamond. In turn, using more accurate measurements, these values are now known for diamond hardness. A Type IIa diamond (111) has a hardness value of 167±6 gigapascals (GPa) when scratched with an ultrahard fullerite tip. A Type IIa diamond (111) has a hardness value of 231±5 GPa when scratched with a diamond tip; this leads to hypothetically inflated values.

Ultrahard fullerite has a hardness value of 310 GPa, though the actual value may range ±40 GPa, since testing done using an ultrahard fullerite tip on ultrahard fullerite will lead to, like diamond on diamond, distorted values. It is thought that beta carbon nitride will have a hardness value, if harder than diamond, less than that of ultrahard fullerite.

C₆₀ has also been used to create an even harder material: aggregated diamond nanorods ^*

Superhard materialsCarbon forms