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Diamond and graphite are two allotropes of carbon: pure forms of the same element that differ in structure. If heated over 700 °C (1,292 °F) in air, diamond, being a form of carbon, oxidizes and its surface blackens, but the surface can be restored by re-polishing. [47]
Diamond is the hardest known material to date, with a Vickers hardness in the range of 70–150 GPa. Diamond demonstrates both high thermal conductivity and electrically insulating properties, and much attention has been put into finding practical applications of this material. However, diamond has several limitations for mass industrial ...
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Diamond is the hardest material on the qualitative Mohs scale. To conduct the quantitative Vickers hardness test, samples of materials are struck with a pyramid of standardized dimensions using a known force – a diamond crystal is used for the pyramid to permit a wide range of materials to be tested. From the size of the resulting indentation ...
Carbonado, commonly known as black diamond, is one of the toughest forms of natural diamond. It is an impure, high-density, micro-porous form of polycrystalline diamond consisting of diamond, graphite , and amorphous carbon , with minor crystalline precipitates filling pores and occasional reduced metal inclusions. [ 1 ]
Diamond (Mohs 10) is 1500 (off scale). Diamond was the hardest known naturally occurring mineral when the scale was designed, and defines the top of the scale, arbitrarily set at 10. The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, or the softest material that can ...
The system of carbon allotropes spans an astounding range of extremes, considering that they are all merely structural formations of the same element. Between diamond and graphite: Diamond crystallizes in the cubic system but graphite crystallizes in the hexagonal system. Diamond is clear and transparent, but graphite is black and opaque.
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.