Carat

Carat, measure of the weight of gems and pearls or of the purity of precious metals. The name comes from the dried seeds of the carob tree, which were used to weigh gold in Africa and diamonds in India. The value of the carat varied from 190 mg to almost 210 mg until 1913, when a standard carat of 200 mg was adopted. As a measure of purity, 1 carat represents 1 part in 24 of the precious metal. Thus 22-carat gold contains 22 parts of gold and 2 of other metal.