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Due to its unique internal structure and powers of light reflection, when cut to proper proportions, diamonds gather light within itself and then sends it back in a shower of fire and brilliance. The life of a polished diamond is regarded as the amount of light that is reflected back to the viewer. The term life is also referred to as brilliance. If the diamond is cut with good proportions then the brilliance will be increased. Lustre refers to the surface gloss on a polished diamond. Fire the play of colours that can be seen from the crown of a polished diamond. As light enters the diamond it is refracted and broken up into the colours of the spectrum and reflected back. The resulting rainbow-like colour flashes are called fire.
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The hardness of diamond is an important property. As an industrial tool it has many uses and modern industry is highly dependent upon it. As a gemstone, it is resistant to scratching and abrasion, which ensures that a finished gem will retain its brilliance and polish. Because of its hardness and the unique way in which it is manufactured, a diamond polishes very slowly. It forms an unusually flat, finely-polished adamantine surface, with very sharp, straight edges between facets. No other gemstone can quite match this standard of polish.

Diamond has the highest coefficient of thermal conductivity of any known substance because the closely-packed crystal structure conducts heat very quickly. The thermal conductivity of diamond is five times higher than that of copper. This explains why a diamond feels cold to the touch when first picked up but quickly becomes warm from the heat of your fingers.
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Only about one-fifth of all mined diamonds could be considered of gem quality. From 40 to 250 tons of gravel and sand must be processed today to recover one rough diamond from the world's thinning diamond deposits. Experts estimate that all known supplies of diamonds will be depleted within 30 to 40 years. 75 - 80% of all diamonds mined are used for industrial applications such as drilling, grinding, or sawing. The remainder are used for jewelery or investment. Less than 2% of the diamonds mined are of such high quality that they may be considered investment quality.
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On average, 250 tons of ore must be mined and processed to produce a one carat diamond of gem quality. When the mining operation is completed, sorters look at rough diamonds, separating them into small piles by shape, size, and quality, a long and laborious process.

The earliest examples of diamonds in human hands were found 3,000 years ago, in India. There, diamonds were used primarily as talismans to ward off evil and protect the wearer in battle. Diamonds were also used by the early Chinese, Greeks, and Romans as an engraving tool. While there was some mystique surrounding diamonds because they were so rare and difficult to obtain-many early cultures believed they had magical properties