Of all the gemstones a diamond is the simplest in composition - it is pure crystalline carbon. Formed billions of years ago deep within the earth's mantle under conditions of extreme temperature and pressure, diamonds are the hardest natural substance known to man. This allows a diamond to achieve an exceptionally high level of polish relative to other gemstones. It also allows it to withstand abrasion and retain its polish.
When a well-cut diamond catches the light, the stunning effect of reflected light accompanied by a play of spectral colours is described by the terms 'fire' and 'brilliance'. The reason for these fabulous light gymnastics stems from the diamond's high refractive index - when light travels from air into the denser medium of diamond, the different spectral colours are slowed down by differing degrees resulting in their separation. When effect of the light exiting the stone in an array of colours is known as 'dispersion'.
The 4Cs - cut, colour, clarity and carat weight - are the characteristics that determine a diamond's rarity and value. They are the four basic industry-accepted grading criteria which determine why two diamonds of equal size may not be of equal value. A basic understanding of each characteristic is therefore important for making an informed purchase decision.
Many consider the cut of a diamond to be the most important of the 4Cs as it is the quality of cut which unlocks a diamond's fiery brilliance. It is the skill of the cutter in proportioning the size and angles of a diamond's facets that will determine the level of beautiful brilliance which meets the eye.
While most diamonds appear white, virtually all display barely imperceptible tints of colour. The grading of a diamond's colour measures the degree to which it approaches colourlessness. White diamonds are the most popular and the most prevalent in jewellery, but it should be noted that some highly desirable stones are coloured pink, blue, yellow or even black.
At the time of a diamond's formation tiny traces of non-crystallised carbon or other minerals and gases may have become trapped inside. These are broadly termed "inclusions" and are often referred to as nature's fingerprints. The clarity grade of a diamond is determined by the presence, size and positioning of these inclusions as they may impede the passage of light through the stone.
The carat is a standard unit of measure equal to 1/5 gram. A carat can be further sub-divided into 100 "points" allowing the easier description of stones weighing less than one carat. It should be emphasised that gem quality diamonds of over one carat are immensely rare - only one in every thousand diamonds polished will be of this size.