Why is the weight of diamonds measured in carats? (3 photos)

The word "carat" comes from Italian. carato, which comes from the Arabic qīrāṭ قيراط, in turn borrowed from the Greek kerátion (κεράτιον) “carob seed”.





The evergreen carob tree or Ceratonia silique is very common in the Mediterranean. Its hard and flat seeds (carob) were used during the Roman Empire as a unit of weight measurement - the kerat, since they weighed consistently 0.19-0.20 g. From the 15th century to today, this is the standard for all precious stones.



Before this, seeds were used wherever there was a need for such precise weight measurement. It was convenient to count them, and due to their hardness, these seeds did not wear off, so the weight remained the same for a long time. So says the legend.



The official metric definition of carat was adopted in France in 1907 and in the USA in 1913: Carat (ct) was equal to 0.2 g.