Carat (ct)
Definition: A carat (symbol: ct) is a unit of mass equal to exactly 200 milligrams, or 0.2 grams. It is primarily used for gemstones and pearls.
History/origin: The carat originated from the carob seed, which was historically used as a rough standard for weighing gemstones because of its relatively uniform size. The metric carat was standardized in the early 20th century.
Current use: Carats are used almost exclusively in jewellery and gem trading to describe the weight of diamonds and other precious stones.
