Diamonds: The Four Cs - Carat Weight

The weight of a diamond, as with all gemstones, is expressed in carats. The word "Carat" is derived from the Greek word “keration” which is also the Greek name for the Carob tree (Ceratonia Siliqua). In the Middle East, this tree is fairly common and produces pods with seeds. Ancient merchants discovered the seeds were always uniform in weight and used them for weighing pearls, diamonds and other precious stones. The weight of one carob seed was later standardized to 1/5th of a gram; hence, a five-carat diamond weighs 1 gram.

A carat is divided into 100 points, so a 1/2 carat stone equates to 50 points, a 1/4 carat diamond 25 points. Very small stones, such as those used in pavé or channel settings, are sometimes called melee. Melees range from .01 to .16 carat in weight. The significance of a diamond's weight, like the other quality grades, is a question of rarity. Out of 250 tons of diamond-bearing ore only a single one-carat diamond of gem quality may be found.

Since diamonds become rarer as they increase in weight, the larger the diamond, the more valuable (and costly) it is. But the price of a diamond does not increase at the same rate as its weight. The larger the stone (all else being equal), the more disproportionate the increase in cost per carat. For example, a 2-carat diamond is always more expensive than two 1-carat diamonds of the same quality. The price of a diamond tends to increase exponentially as the size increases.