What is the difference between carats in diamonds and karats in gold?

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The carat is a unit of mass equal to 200 mg (0.2 g; 0.007055 oz) and is used for measuring gemstones and pearls. The current definition, sometimes known as the metric carat, was adopted in 1907 at the Fourth General Conference on Weights and Measures[citation needed], and soon afterward in many countries around the world.[1] The carat is divisible into one hundred points of two milligrams each. Other subdivisions, and slightly different mass values, have been used in the past in different locations. http://en.wikipedia.org/wiki/Carat_(mass) The karat or carat (symbol: K or kt) is a unit of purity for gold alloys... Therefore, 24-Karat gold is fine (99.9% Au w/w), 18-Karat gold is 18 parts gold 6 parts another metal (forming an alloy), 12-Karat gold is 12 parts gold (12 parts another metal), and so forth. http://en.wikipedia.org/wiki/Carat_(purity) Jan 11 12, 6:16 PM