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In diamond, all the carbon-to-carbon bonds, both within a layer of rings and between them, are in the staggered conformation, thus causing all four cubic-diagonal directions to be equivalent; whereas in lonsdaleite the bonds between layers are in the eclipsed conformation, which defines the axis of hexagonal symmetry.
Lonsdaleite is an allotrope sometimes called "hexagonal diamond", formed from graphite present in meteorites upon their impact on the earth. The great heat and pressure of the impact transforms the graphite into a denser form similar to diamond but retaining graphite's hexagonal crystal lattice .
Diamond and graphite are two allotropes of carbon: pure forms of the same element that differ in crystalline structure.. Allotropy or allotropism (from Ancient Greek ἄλλος (allos) 'other' and τρόπος (tropos) 'manner, form') is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements.
Diamond is the allotrope of carbon in which the carbon atoms are arranged in the specific type of cubic lattice called diamond cubic. It is a crystal that is transparent to opaque and which is generally isotropic (no or very weak birefringence). Diamond is the hardest naturally occurring material known.
In 2001, a diamond-like-structured c-BC 2 N was synthesized at pressures >18 GPa and temperatures >2,200 K by a direct solid-state phase transition of graphite-like (BN) 0.48 C 0.52. The reported Vickers and Knoop hardnesses were intermediate between diamond and c-BN, making the new phase the second hardest known material. [39]
A diamond simulant is a non-diamond material that is used to simulate the appearance of a diamond, and may be referred to as diamante. Cubic zirconia is the most common. The gemstone moissanite (silicon carbide) can be treated as a diamond simulant, though more costly to produce than cubic zirconia.
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