Heat Treated Garnet

[Capitol Bill]

Just attended our monthly GIA Alumni meeting here in the DC area last night. Richard Drucker was our guest speaker and he had lots of great information in his presentation. One of the interesting things he mentioned was that his lab has seen a few heat treated demantoid garnets. I thought this was an interested bit of info to pass along since most of us (well, at least me) would have never thought to check a garnet for heat.

Regards,
Bill Scherlag

 

[Richard M.]

This is pretty well known, Bill. Most sellers of demantoid routinely list heat as a normal enhancement for the stone per the AGTA guidelines. Many demantoids are not heated, but I don''t know of a reliable way of making the distinction. Only low heat is involved and the color improvement is permanent.

Richard M.

 

[Capitol Bill]

Thanks for the info, Richard. I guess I haven''t dealt with demantoid enough to know this. Richard Drucker seemed to imply that this is a relatively new phenomenon, but perhaps I was mistaken in the way I heard it.

Kind regards,
Bill Scherlag

 

[Richard M.]

Hi Bill,

These data are taken from a Pala Gems article on demantoid written in 2002. But the heat treatments have been known to specialists for many years. It may be that the information is just getting out to the broader public.

Regards

Richard M.

Properties of Demantoid Garnet
Demantoid Garnet (a variety of andradite garnet)
Composition Ca3Fe2(SiO4)3
Hardness (Mohs) 6.5 to 7
Specific Gravity 3.84
Refractive Index 1.888; Singly refractive
Crystal System Cubic
Colors

Light to deep green
Pleochroism None
Dispersion 0.057; this is among the highest of all gems, even higher than diamond
Phenomena None
Handling Ultrasonic: generally safe, but risky if the gem contains liquid inclusions
Steamer: not safe
The best way to care for demantoid garnet is to clean it with warm, soapy water. Avoid exposing it to heat or acids.
***Enhancements Some demantoid is heat treated to improve the color***
Synthetic available? No

 

[flamingogirl]

hi--I have been searching for a demantoids myself and have on rare occasion found some treated ones--which I don''t know what to make of since they are not supposed to be. and this was from the top suppliers. these stones happen to be particularly high grade expensive ones. so it is a bit confusing when you are looking for the best, I am definitely left pondering...

 

[MJO]

Date: 4/30/2006 11:10:47 PM
Author: flamingogirl
hi--I have been searching for a demantoids myself and have on rare occasion found some treated ones--which I don''t know what to make of since they are not supposed to be. and this was from the top suppliers. these stones happen to be particularly high grade expensive ones. so it is a bit confusing when you are looking for the best, I am definitely left pondering...

Heat treating garnets is only done for demantoid as far as I know. I don''t even beleive you can tell but a good supplier will let you know if he know.

Regards,
Maurice