A diamond is a crystal made up entirely of carbon atoms that are arranged in an isometric, or cubic, matrix. A cubic crystal arrangement is one in which the crystal essentially expands outward at the same rate in all directions during its initial growth; the ideal result, when the crystal forms without any interference, is a pure and perfectly formed octahedral shape.
However, most diamond crystals encounter varying heat or pressure, other elements, or even other diamond crystals during their growth, and this can alter their form somewhat. The resulting form and characteristics of the crystal, once it emerges from the earth, help to determine what shape, color and clarity the polished gem will have.
The combination of diamond’s molecular composition and its crystal structure is what makes it so unique and gives it all the qualities that we think of when we think of a diamond.
Consider this: The graphite that you commonly find in pencils is also made of pure carbon, but because the carbon atoms are arranged differently, the result is a soft gray-black substance that is very unlike hard, colorless diamond. And iron pyrite (known more commonly as “fool’s gold”) grows in an isometric arrangement, but because it is not made of pure carbon, it also lacks the spectacular qualities of diamond.
The unique characteristics of diamond go far beyond what you can see with your eye. In addition to their superior brilliance and dispersion, diamonds are the hardest natural substance on earth.
Diamond rates a 10 on the Mohs scale of hardness, which means that it is extremely resistant to scratches; it is several times harder than the next-hardest substance, corundum, which is more commonly known as ruby and sapphire.
Diamonds are also very tough, meaning that they do not easily break, chip or crack. And even more interestingly, they are extremely resistant to heat and chemicals: it would take a temperature of at least 720° Celsius in air, or 850° Celsius in a vacuum, to burn a diamond; and sulphuric and hydrochloric acids, which are capable of completely dissolving the skin and bones of a person, have no effect at all on diamonds (in fact, these acids are actually used to clean the oil and dust off polished diamonds after they have been cut).