About Diamonds

A diamond is a transparent crystal of tetrahedral bonded carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. The chemical bonds that hold the carbon atoms in diamonds together are weaker than those that hold together the other form of pure carbon, graphite. The difference is that in diamonds, the bonds form an inflexible three-dimensional lattice. In graphite, the atoms are tightly bonded into sheets, which can slide easily over one another.

In particular, diamond has the highest hardness and thermal conductivity of any bulk material. Those properties determine the major industrial application of diamond in cutting and polishing tools.

Diamond has remarkable optical characteristics. Because of its extremely rigid lattice, it can be contaminated by very few types of impurities, such as boron and nitrogen. Combined with wide transparency, this results in the clear, colorless appearance of most natural diamonds. Diamond also has relatively high optical dispersion that is the ability to disperse light of different colors, which results in its characteristic luster. Excellent optical and mechanical properties, combined with efficient marketing, make diamond the most popular gemstone.

Hardness
Diamond is the hardest natural material known, where hardness is defined as resistance to scratching and is graded between 1 (softest) and 10 (hardest) using the Mohs scale of mineral hardness. Diamond has a hardness of 10 (hardest) on this scale. Diamond's hardness has been known since antiquity, and is the source of its name.

Diamond hardness depends on its purity, crystalline perfection and orientation: hardness is higher for flawless, pure crystals oriented to the direction (along the longest diagonal of the cubic diamond lattice). Therefore, whereas it might be possible to scratch some diamonds with other materials, such as boron nitride, the hardest diamonds can only be scratched by other diamonds. In particular, nanocrystalline diamond aggregates were measured to be harder than any large single crystal diamond.

The hardness of diamond contributes to its suitability as a gemstone. Because it can only be scratched by other diamonds, it maintains its polish extremely well. Unlike many other gems, it is well-suited to daily wear because of its resistance to scratching—perhaps contributing to its popularity as the preferred gem in wedding rings, which are often worn every day.

Electrical conductivity
Diamonds can be identified by their high thermal conductivity. Other specialized applications also exist or are being developed, including use as semiconductors: some blue diamonds are natural semiconductors, in contrast to most diamonds, which are excellent electrical insulators. The conductivity and blue color originate from boron impurity. Boron substitutes for carbon atoms in the diamond lattice, donating a hole into the valence band.