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The C₆₀ fullerene in crystalline form

Fullerites are the solid-state manifestation of fullerenes and related compounds and materials.

Polymerized single walled nanotubes (P-SWNT) are a class of fullerites and are comparable to diamond in terms of hardness. However, due to the way that nanotubes intertwine, P-SWNTs do not have the corresponding crystal lattice that makes it possible to cut diamonds neatly. This same structure results in a less brittle material, as any impact that the structure sustains is spread out throughout the material. Because nanotubes are still very expensive to produce in useful quantities^{[citation needed]}, uses for a material lighter and stronger than steel will have to wait until nanotube production becomes more economically viable.

Ultrahard fullerite (C₆₀) is a form of carbon which has been found to be harder than diamond, and which can be used to create even harder materials, such as aggregated diamond nanorods. It therefore exhibits a hardness higher than a 10 on the Mohs hardness scale.

Specifically, it is a unique version of fullerene (which is a class of spherical, ellipsoidal, or tubular carbon molecules) with three-dimensional polymer bonds. This should not be confused with P-SWNT fullerite, which is also a polymerized version of fullerene. It has been shown^[1][2] that when testing diamond hardness with a scanning force microscope of specific construction, ultrahard fullerite can scratch diamond. In turn, using more accurate measurements, these values are now known for the hardness of diamond. A Type IIa diamond (111) has a hardness value of 167±6 gigapascals (GPa) when scratched with an ultrahard fullerite tip (the hardness of a substance can only be tested properly with a harder substance). 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^[3].

• Carbon nanotube

1. ^ Nano-sclerometry measurements of superhard materials and diamond hardness using scanning force microscope with the ultrahard fullerite C60 tip
2. ^ Ultrahard and superhard phases of fullerite C60: comparison with diamond on hardness and wear
3. ^ Diamonds lose 'world's hardest' title

• Introduction to fullerites
• Introduction to P-SWNT