|1.||a measure of the weight of precious stones, esp diamonds. It was formerly defined as 3.17 grains, but the international carat is now standardized as 0.20 grams|
|2.||Usual US spelling: karat a measure of the proportion of gold in an alloy, expressed as the number of parts of gold in 24 parts of the alloy|
|[C16: from Old French, from Medieval Latin carratus, from Arabic qīrāt weight of four grains, carat, from Greek keration a little horn, from keras horn]|
unit of weight for diamonds and certain other precious gems. Before 1913 the weight of a carat varied in different gem centres. Originally based on the weight of grains or leguminous seeds, which, of course, varied in size from place to place, the carat was equivalent to 0.2053 gram (3.168 troy grains) in London, 0.1972 g in Florence, and 0.2057 g in Amsterdam. The weight of a gemstone was calculated in terms of whole carats plus fractions (12, 14, 18, 116, 132, or 164) of a carat; thus, a stone might be said to weigh 3 + 14 + 116 carats. After various unsuccessful attempts to standardize the carat, the metric carat, equal to 0.200 g, and the point, equal to 0.01 carat, were adopted by the United States in 1913 and subsequently by most other countries. The weights of diamond, ruby, sapphire, emerald, topaz, aquamarine, garnet, tourmaline, zircon, spinel, and sometimes opal and pearl are expressed in carats
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