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 Weights used in the gem trades

Optical properties

Carat The weight used in the gem trade since antiquity. The name is derived from the seed (kuara) of the African Coraltree or from the kernel (Greek -kertion) of the Carob bean. Since 1907 Europe, as well as America, has adopted the metric carat of 200mg or 0.2g. Therefore weights given for famous old diamonds often vary because local carats and not metric carats were used. The carat is subdivided into fractions (l/10ct) or decimals (1.25ct) up to two decimal places. Small diamonds are weighted in "points" = l/100cts (=0.0lcts). The table below illustrates diameter and corresponding carat weight for diamonds cut in the modern brilliant cut (p. 81). Gems with different specific gravity and different cuts obviously have different diameters designer diamond wedding rings. The carat weight of gems is not to be confused with the carat used by the goldsmith. In the case of gold the carat is no weight measure but a designation of quality. The higher the caratage, the higher the content of gold in the piece of jewelry. The weight can be variable.
Gram Weight used in gem trade for less precious stones and for rough stones (for instance quartz).
Grain (Latin - granum) Weight measure for pearls. Corresponds to 0.05 grams = 0.25 or \ carat. Increasingly superceded by carat weights. The old Japanese weight of Momme (=3.75 grams= 18.75 carats) is hardly used any more in Europe.
Prices in the Gem discount engagement rings Trade The price quoted is always the carat price. This has to be multiplied by the actual weight to obtain the price of the particular stone. The price quoted to the final buyer is often the total price. With diamonds the price per carat increases progressively with the size of the gem in very small steps, 10 points with more expensive stones. If, for instance, a one carat stone costs £750/$1275, a two carat stone (of the same quality) does not cost £1500/$2550 per carat, but maybe £2500/14250 or more. Colored stones have fixed carat prices for much bigger size groups.