Carat: Diamonds and other precious gems are valued on weight, or carats. A carat is 1/5 of a gram. Sometimes diamonds under a carat are valued in points. One carat is 100 points, so a quarter carat diamond can be referred to as 25 points. Diamonds are not valued on their apparent size, since the size can be either enhanced or diminished by the cut. for example: A broad cut shallow diamond would look larger than a traditional round cut but would weigh the same. The offset to cutting a diamond to look larger is that some brilliance may be lost. Different gemstones have different densities. An emerald is lighter than a diamond and a ruby is heavier. A one carat diamond, one carat emerald, and one carat ruby would be three different sizes if they were all identical shapes and cuts.
The more the diamond weighs the more valuable it is. The price of a diamond is based on carats, but the more the diamond weighs, the higher price it has per carat, all other things being equal, meaning the diamonds are the same in color, cut and clarity. In other words, a one carat diamond may be priced at $10,000 per carat, while a two carat diamond will be priced at $20,000 per carat. The one carat diamond costs $10,000 and the two carat diamond costs four times as much or $40,000. The discrepancy increases the higher the carat weight.
Diamonds of one carat or more can be graded by an independent lab as to the quality of the cut, weight, color, and clarity. The certificate is often available at the diamond seller’s.
When you’re buying a diamond you can choose which factors are more important to you. If you want more carats, you can trade off clarity. If it’s important the color is as close to pure white as possible, you can get a stone weighing less carats, or perhaps one that has a minor, but not visible to the naked eye imperfection. If you want the look of a larger diamond consider clustering 5 or 7 smaller diamonds in the place of larger stone.
Just in case you're interested the largest diamond ever found on earth is the 530 carat Star of Africa, that's about the size of a large chicken egg and was cut from a 3,100 carat rough stone. That stone produces 9 other gem quality diamonds. It resides in the crown jewels in