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It is isostructural with Si 3 N 4 and was predicted to be harder than diamond. [35] The calculated bond length was 1.47 Å, 5% shorter than the C-C bond length in diamond. Later calculations indicated that the shear modulus is 60% of that of diamond, and carbon nitride is less hard than c-BN. [36]
Lonsdaleite (named in honour of Kathleen Lonsdale), also called hexagonal diamond in reference to the crystal structure, is an allotrope of carbon with a hexagonal lattice, as opposed to the cubical lattice of conventional diamond.
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Its color ranges from black to brown and gold, depending on the chemical bond. It is one of the hardest known materials, along with various forms of diamond and other kinds of boron nitride. Borazon is a crystal created by heating equal quantities of boron and nitrogen at temperatures greater than 1800 °C (3300 °F) at 7 GPa (1 million lbf/in 2).
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Maximum pressures measured using current experimental techniques are around 55 GPa. However, these new superhard phase nanotubes collapse at an even higher, albeit unknown, pressure. [citation needed] The bulk modulus of superhard phase nanotubes is 462 to 546 GPa, even higher than that of diamond (420 GPa for single diamond crystal).
The collision of a dwarf planet and an asteroid 4.5 billion years ago resulted in space diamonds in meteorites eventually landing on Earth.
Cubic zirconia is relatively hard, 8–8.5 on the Mohs scale—slightly harder than most semi-precious natural gems. [1] Its refractive index is high at 2.15–2.18 (compared to 2.42 for diamonds) and its luster is Adamantine lustre. Its dispersion is very high at 0.058–0.066, exceeding that of diamond (0.044).