Diamond carat wt vs. coloured stones

[bstraszheim]

Good morning everyone : )

First of all a great big thanks to Pricescope and all the posters, what a wealth of information and help. This is my first post but I''ve been reading avidly for about a month - yeah I know, chicken feed compared to most here, but it''s a start!

I am curious about how diamond carat weights compare to coloured stones, say for instance, aquamarines and sapphires. If you had round 1 carat diamond, would an aquamarine/ saphhire of the exact same proportions also weigh 1 carat? If not, what stone comes the closest to a diamond in terms of carat for carat weight?

I wish you well,

Bridget

 

[strmrdr]

There is so much variation in how gemstones are cut that you cant really go by weight you have to go by diameter.
There are literly thousands of different cuts for gemstones just in the round shape that it makes the question really impossible to answer in a real world setting, each cut would have a different weight for any given diameter.

 

[Richard M.]

Yes, cut can affect the apparent size of similar-weight stones -- even diamonds -- and those are good points strmdr. But there's a another factor: specific gravity or density.

Just as a pound of lead takes up less volume than a pound of feathers because it's more dense, a one carat sapphire will be smaller than a one carat diamond (assuming cuts are identical) for the same reason. Sapphire's S.G. is roughly 4.0 while diamond is about 3.5.

All gem minerals have their own S.G.s based on chemistry. To answer Bridget's bottom-line question, gems that have S.G.s close to diamond are Benitoite, Pyrope and Grossular garnet, Spinel, Topaz, Kyanite, and rare ones from Sri Lanka like Taafeite and Sinhalite. Tanzanite's fairly close at 3.35.

But that's where cut comes into play. A diamond that weighs one carat can be shallow and wide, narrow and deep, or cut to correct proportions. It's the same with all other stones. "Correct" proportions have to do with the way light behaves inside the stone to reflect as much brilliance back to the eye as possible. These are all generalizations

of course, but this is the short version.

Richard M.

 

[WinkHPD]

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On 6/24/2004 9:33:35 AM bstraszheim wrote:

If you had round 1 carat diamond, would an aquamarine/ saphhire of the exact same proportions also weigh 1 carat?
Bridget----------------

An aquamarine of the exact same proportions would weight less than one carat and a sapphire would weigh more. Sapphire has a specific gravity of 4.0 versus the 3.52 of diamond. The specific gravity of aquamarine is less than that of diamond, my brain keeps saying 2.58 but I am working from tired memory this morning and the chart is at the office so I am flying without a net here. These are not numbers I use every day, so please, no whipping if I am off a little on the aqua.

Wink