MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY
Seeds of the carob tree - Ceratonia siliqua - were used for centuries to weigh gems, famously diamonds, because the small brown seeds are uniform in weight. Carob evolved into carat. However, the weight of the seeds varies according to where they grow in the Mediterranean. The metric carat,.200 grams, was only adopted in 1907 at the Fourth General Conference on Weights and Measures, and soon afterwards in many countries around the world. The weights of diamonds, rubies, sapphires, emeralds, topaz, aquamarines, garnets, tourmalines, zircons, spinels, and, sometimes, opals and pearls are expressed in carats. Prosaically, the bean pods are often used as animal fodder and the seeds ground to a flour can be used for cooking and a chocolate replacement. Languedoc, France, Europe.
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