Weight of sapphire (corundum)

[Cyren]

Hoping someone can answer this for me: are diamond and sapphire (corundum) similar is density? Thus, for the same carat weight, are diamonds and sapphires similarly sized?

“Spread” after cutting aside, are the rocks going to equal each other? The question is academic, as most people will look at both carat weight and spread when choosing any gem, but I’m curious.

Thanks!

 

[Dee*Jay]

Sapphires are about 30% denser than diamonds so a sapphire of the same ct weight will be about 2/3 the size of a diamond of the same ct weight (all other things being equal).

 

[Cyren]

Thanks DeeJay. I remember someone mentioning this on the board in passing, but I wanted a definitive explaination.

 

[colorchange]

Date: 2/14/2007 12:50:22 PM
Author: Dee*Jay
Sapphires are about 30% denser than diamonds so a sapphire of the same ct weight will be about 2/3 the size of a diamond of the same ct weight (all other things being equal).

Beeing a bit more accurate:
Sapphire density is 4, diamond is 3.52. sapphire is only 14% more dense.
So a 3.52 Ct diamons and a 4 Ct sapphire of same cut (which is very unusual) would make the same size.
A sapphire of 3.52 Ct would be (3.52/4)^(1/3) that is 4.2% smaller if you consider diameter for instance.
If the diamond is 9 mm, the sapphire will be 8.6 mm.
If you consider face surface (what we perceive as size), sapphre will be 8.2% smaller.

Since refractive index of sapphire is lower, a diamond cut sapphire has to be deeper.
And sapphire is almost never cut that way.

 

[Dee*Jay]

Colorchange, thanks for giving better info! I don''t know where I got 30% from; my apologies for misleading you Cyren.

 

[Richard Sherwood]

Although it is only 14% denser than diamond (as Colorchange points out), in actuality a sapphire of the same millimeter measurement will usually weigh 30% more than a diamond, sometimes as much as 40% (as DeeJay points out).

This is because of the difference in cutting between sapphire and diamond. Diamond is much more precision cut, while sapphire has usually thicker girdles, larger "bulge" factor, etc.