Worlds of David Darling
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A carat is a unit of mass used for weighing precious stones. Since 1913 the internationally accepted carat has been the metric carat (CM) of 200mg. The purity of gold is also expressed in carats (usually spelled "karat" in the United States). Here one karat is a 24th part; thus, pure gold is 24-karat; "18-karat gold" contains 75% gold and 25% other noble metals, and so on.

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