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A diamond is the most concentrated and portable thing of value known to man. A stone the size of a walnut can be worth millions of dollars. Because most diamonds - even many very valuable ones - weigh considerably less than an ounce, they require a special unit of weight. That unit is the carat, equal to 1/5th of a gram and divided into 100 equal parts called points. Thus a gem listed as, say, 1.03 carats weighs 103 points.
 The term carat is derived from the Greek word, ket- ation, for the carob tree. Found throughout the Mediterranean region, carob tree seeds were ideal for expressing gemstone weight eons ago because they are extremely light and fairly uniform in weight. Nevertheless, it wasn't until early in this century that universal agreement was reached on the exact weight of a carat: 200 milligrams. Until then, a carat equaled anything from 188 to 214 milligrams, depending on the country. That's why all of the world's famous diamonds have been taken out of their mountings in recent years and re-weighed using electronic scales with digital readouts that are accurate to the hundredths of a milligram.
Although the trade uses fractional units, it does not mean all diamonds are priced the same that fall within them. All other things being equal, a diamond weighing 0.71 carat will cost less than one weighing 0.84 carat, although both fall within the three-quarter carat Category. Also, diamonds in one general weight category will cost more than those in the preceding one, even when the difference in weight is a point or two.
So, for example, there can be a significant difference between the per carat cost of a diamond just below and just over one carat. Because of such a difference, it is always best to know the exact weight of a diamond. In most cases, determining the exact weight is easy because diamonds are weighed loose before being mounted. But in those cases where they weren't, there are formulas for computing accurate weights. |
