Diamonds were formed deep within the Earth's crust under intense heat and ressure billions of years ago. Some were even brought to earth in meteorites from outer space. They are the hardest gemstone, more than a thousand times harder than an emerald. They are, in fact, the hardest natural substance known to man. This hardness is a result of their high density, and itis this density that makes them so brilliant - light passes through them more slowly, refracting as it passes from the air into and out of the diamond. Diamonds also have the ability to separate (disperse) light into the colours of the rainbow, so that when properly cut, they produce more fire and brilliance than other gemstones. Although diamonds are found in many locations in the world, they are expensive to mine. In fact, diamonds are the lowest-volume highest-value product on earth - the average yield is a handful of gem-quality diamonds from a pile of ore the size of a house. When a diamond is cut from the rough, approximately half the weight of the original stone is lost. On average, it takes an experienced craftsman a full day to cut and polish 58 facets onto a one-carat stone. A diamond cutter undergoes four years of training to become skilled at his craft, and it takes almost double that time to become a master cutter.