[kar-uh
t] 
| 1. | a unit of weight in gemstones, 200 milligrams (about 3 grains of troy or avoirdupois weight). Abbreviation: c., ct. |
| 2. | karat. |
| car·at (kār'ət) n. Abbr. c or car.
[Middle English, from Old French, from Medieval Latin quarātus, from Arabic qīrāṭ, weight of four grains, from Greek kerātion, a weight, diminutive of keras, kerāt-, horn; see ker-1 in Indo-European roots.] |
| kar·at also car·at (kār'ət) n. Abbr. k or kt. A unit of measure for the fineness of gold, equal to 1/24 part. Pure gold is 24 karat; gold that is 50 percent pure is 12 karat. [Variant of carat.] |
karat
carat
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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