The unit of measurement used for gemstone weight is the carat (ct) used in trade since ancient times. The word derives from the Greek and means ”carob seed” which was used as a measuring unit in weighing gems.
One carat equals exactly 1/5 of a gram, which is 0.2 grams.
It is normal to think therefore that the higher the number of carats, the higher the price of the gemstone.
This is not always true!
Which of these two rings do you think is worth more?
- The ring with 12 emeralds with a total weight of 1.5 carats.
- the solitaire ring with a 1 carat emerald.
The single one-carat gemstone of equal quality is worth much more because large gemstones from one carat upwards are less available and more limited than the others.
If we take gemstones of the same quality we can say that:
“The carat weight of an individual gemstone increases together with the size of its crystal and therefore its rarity”
The price of a gemstone is always calculated as cost per carat:
Total cost of the gemstone/carat weight = cost per carat
The cost per carat of a gemstone does not increase linearly with gemstone weight, as it usually undergoes an exponential increase according to different carat weight intervals.
Attached to this handbook, there is a price list of gemstones that we deal more frequently. This price list may be subject to periodic changes dictated by the market. Through the years, fine quality gemstones generally increase in value thanks to increasing demand and difficulties in finding new sources of extraction.
Size versus carat weight
Sizes of cut gemstones are generally proportional to their carat weight, but this is not a rule because it mainly depends on the cut. A thick gemstone or a gemstone with a very high pavilion can appear smaller than a gemstone cut with a larger table.
This subject, however, falls into gemstone cut category that we will deal with later.
We must also point out that gemstones of the same weight can vary in size depending on their mineralogical species. A two carat weight emerald will in fact be larger than a ruby of the same weight. This is due to the higher density of corundum / ruby compared to beryl / emerald.