As with all precious stones, the weight of a diamond is expressed in carats. the word carat originates from a naturally occurring unit of weight - the seed of the carob tree. Diamonds were traditionally weighed against these seeds until the system was standardised, and one carat was fixed at 0.2grams (one fifth of a gram). One carat is divided into 100 points so that a diamond of 25 points is designated as a quarter of a carat or 0.25 carats.

Diamonds are so rare because only a few survive the hazardous journey from the depths of the earth to reach the surface, and although diamonds are rare, those considered suitable for polishing are rarer still. In fact of those that are made into jewellery, fewer than 5% will be larger than 1 carat.

Diamonds are all the more valuable because recovering the relatively small quantities of gem quality and industrial diamonds that are known to exist is not at all easy, even with the increasing sophistication of today's technology.

Approximately 250 tons of ore from the average kimberlite pipe must be mined and processed in order to produce a one carat polished diamond of gem quality.

Guide only.