Carat is unit of measure.
A little of history, Greek peoples, had for unit of measure the “Keration”. With the shape of the seedpods of the carob tree, Seeds that are small and uniform. They used this reference like unit of measure. Afterward it is Arabic peoples that used it under name “Qirat”. Moreover it is Italian peoples that used it under name “Carato”. Finally, definitely adopted by British peoples in the mid 15th century, under name “Carat”.
the English carat word comes from Greek word “keration”, referring to the shape of the seedpods of carob tree.
It is the unit of measure about gemstones, It is partly that we estimated that value. Of course there are others criterion to consider, like clarity, color and cut and others standard but less important.
1 carat = 0.20 grams so in 1 gram there are 5 carats
To have an estimate on the price by the carat weight you can used this formula. However, it is not to consider the rest of criterion (clarity, color and cut).
It is called “Indian law” or/and “Tavernier law”.
Grams² x Carat = Gemstone price
Also, you need to know the size is different to weight for each gemstones. Even though, the size is a big factor to change weight, some gemstones does not the same weight.
Take an example : one millimeter cubic of Sapphire will be twice as heavy as one cubic of Opal.
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