The "carat" is a unit of mass used for gemstones. The word "carat" comes from the Arab word Kharoub, as the Carob tree (and specifically carob seeds) was used as a benchmark in terms of weight.
Former diamond dealers still call a 1-carat diamant a "four-grain diamond", i.e. it weighs the equivalent of 4 carob seeds.
In 1907, the metric carat was established as being equal to 200 mg or 5 carats = 1 gram.
Diamonds are cut into an infinite number of different cuts, the main ones being:
The cut of the diamond is graded from "excellent" to "poor", according to the criteria for proportion, symmetry and polish
Diamonds are colourless or almost colourless, but they are colour graded from D (absolutely colourless) to Z (noticeable colour).
These are followed by fancy coloured diamonds, the most common of which are brown, yellow, green, and ending with the rarest, such as blue or red.
Diamonds are clarity graded from Flawless with no inclusions (FL) to included3 (I3) with numerous inclusions.