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Gem weight in ready made jewelry

When evaluating jewelry how does one determine the carat weight of a gemstone included in a particular piece without dismantling it gem by gem?

I have a simple tool that I use when I’m in the field that has just about every stone shape and size that gives me the approximate carat weight of a stone. These tools are pretty accurate on modern cut stones. Other than that you would measure the stone and just do the simple math of the stones cut. It all depends on the cut of the stone. I don’t have the variations on hand at this moment. They are easily found.

Hello IMDone,

If you know the identity of the gemstone and the type of cut, and if you can measure its dimensions, you can use some formulas to estimate its carat weight. You’ll need to look up the specific gravity of the gemstone.

Here is an article that explains the procedure.

Hope this helps,
IGS Admin

So in short you can calculate the carat weight of an oval citrine by multiplying the volume times the SG times .002?

I don’t think “diameter x diameter x depth,” where the diameter is the average of the diagonal, length, and width, equals the volume of an oval “ellipsoid.” (But I’m not sure about that). Otherwise, the formula is diameter x diameter x depth x SG of citrine x .002.

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See this is the sort of stuff they should be teaching in high school and how to do your taxes. Its absolutely pointless to calculate the speed and destination arrival times of trains when you consider that we’re at the mercy of the conductor and his own schedule which is more often than not a completely different schedule than the one suggested by the rail line. Jewels and taxes, that’s where it’s at. Now where did I put that Geometry for Dummies book? Thanks for the input men. The formula works. You’re an asset to the field, Much appreciated

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Do you know of any phone apps that might help me in the field?

As far as phone apps…I’m tech lost! I do not believe there is one but if there is I would love to know also. I have been using my templates and doing the calculations and coming pretty close in the field. knowing the SG of your stones will be a great help in this. Zircon would be the on stone that can throw you off due to its popularity and SG.
All the best,

Otter, I did find this site that I can access on my phone when WiFi is available and curious to know what you think of it in terms of accuracy.

So as far as tech goes… on my i phone i have the IGemology app… which has a calculator in it that factors size and gravity of stone and gives you an estimate. its like 15 dollars to own however since you are in the gem industry its a tax write off for tax season. If your worried about the 15 bucks lol.

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During these times $14.98 would have been okay but $15 seems way out of my league. LOL Thanks for the tip.

I wanted an easy solution to this and other problems, my hunt led me to ‘Gemology Tools Professional’ great program with a host of info and tools. Worth checking out and no I don’t have anything to do with the company

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Thanks for the tip! This is great stuff.

What is the easiest way to calculate the ct weight of Citrine in these carved stones? There are three individual carvings? Measurements are 12x12.1x6mm for the flower, 14.1x11.25x3.7mm for one leaf and 13.3x9.6x3.7mm for the other leaf. Do I base them on Cabs?