Carat is the unit used to express the weight of gemstones, with one carat equal to 200mg of actual weight.
From the History of the Carat
It is supposed that the word carat derives from cuara - the name of the African coral tree, the seeds of which were used as weights for weighing of the gold sand. However it’s more likely that it’s connected with the name of the seeds of the Mediterranean carob tree, as they are practically equal in weight. They were used as weights for gems weighing. Their weight was about 200mg and that was one carat.
The centers of the jewelry’s business had their own mass measures.
So, the London carat was equal to 205,3mg, the Florentine one - 197,2mg. It explains the difference in the weight of historical diamonds. The metric carat was introduced in 1907 in Paris. It is equal to 200mg. That is what we have now.
Other Gemstones Weight Units
The gram is a weight unit that is used for less expensive and rather small gems.
The grain is used to weigh pearls. It is equal to 14 of the carat, i.e. 50mg. It is seldom used nowadays.
How to Calculate the Price of a Gemstone
In the gems trade the price of 1 carat is indicated. If you want to calculate the full price of a stone you should not multiply the price of a carat by the stone weight in carats. The price of a carat rises progressively with the increase of the stone size. Say, if a diamond weighing less than 1 carat costs X, a diamond with the mass of 2 carats doesn’t cost 2X, but much more.
In any case, the price of a stone is largely influenced by its quality, clearness, color intensity, latent and obvious defects, the quality and the style of the framing. That is why when it comes to jewelry it’s not at all only about maths .
Birthstone for May
That is what we have now.
"Not a bad thing to know when you are buying your girlfriend a birthstone for May."
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