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 Post subject: Article about chrome bearing Grossular with some andradite
PostPosted: Sat Dec 12, 2009 3:49 am 
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Hello,

As I found some interesting garnets..
I did an article on a chromium colored grossular that contain some andradite.
The article is in french but I did an abstract in english and there is some photos and figures.

Feel free to download/read this n° 40 of the article rubric from GI.com

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PostPosted: Sat Dec 12, 2009 8:10 pm 
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hi gemca, since i cannot read french, is the study on grossular garnet, particularly the green grossular that contains chromium?, have similar composition to the andradite/grossular found in mali?? :oops: i was able to read the abstract of the article since it is in english. :wink:


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PostPosted: Sun Dec 13, 2009 12:07 pm 
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Hi,
Yes the article report some green grossular garnet that are colored by chromium and contain a compositional andradite part (like some grossular-andradite that are fond in Mali).

This type of garnet give bright intense green stone.

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PostPosted: Sun Dec 13, 2009 1:57 pm 
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Hey,
Can you elaborate on the treatment done on the mali garnets.Thanks

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PostPosted: Sun Dec 13, 2009 2:28 pm 
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Can you let us know the source, Jean-Marie?

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PostPosted: Sun Dec 13, 2009 9:56 pm 
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:? i'm confused, mali garnets are not being heat treated are they??


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PostPosted: Mon Dec 14, 2009 3:46 am 
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My mistake i guess...i thought that mali garnets are being treated with chrome bearing substances for them to represent demantoid...however is such a treatment possible?

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PostPosted: Mon Dec 14, 2009 7:59 am 
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Hi,

ROM, I don't know the locality.
A sample was given (the Xtal) and another loan from my friend Roberte.
I bought the third sample at a pakistani rough dealer.. but I don't know wether this sample was from Pakistan or not...:s

Vismay,Gingerkid, sorry if my english could mislead you.

Actually, the studied samples are natural and (most probably) untreated.

I don't think possible to perform heat treatment on a garnet without damaging it (my guess and according to a bibliography published in Journal of Gemmology obout the heating of some garnet).

Actually, this material interested me because it has a composition like the one of some "Mali garnet" (i.e. Grossular mixed with some andradite), thus it has a higher refractive index than for "normal grossular". And, finally, it has coloration that is gave by chromium (instead of vanadium for the majority of green grossular / Tsavorite garnets).

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PostPosted: Mon Dec 14, 2009 9:56 am 
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Hey Gemca,
I got it know that these garnets which you are talking about represent those found in mali (grandite garnet)..do let us know if you get info about which mines they are from...also do u get a mixture of hessonite garnet along with the green grossular??
It is also worth noting that i have not seen mali garnets containg chromium...does anyone know about mali garnet with chromium?

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PostPosted: Mon Dec 14, 2009 2:02 pm 
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I've had some information regarding these "chrome bearing grossular-andradite ". They probably come from Mali.

It seems that, to date, grossular-andradite mixture (with or without chromium) come only from Mali.

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PostPosted: Mon Dec 14, 2009 3:07 pm 
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Gemça wrote:
I've had some information regarding these "chrome bearing grossular-andradite ". They probably come from Mali.

It seems that, to date, grossular-andradite mixture (with or without chromium) come only from Mali.


That's interesting -- thanks. Rouse reported grossular-andradite occurrences from other locations but all appear to be in the Fe-influenced hessonite color range, not green.

A chart on page 93 of his book "Garnet" details such occurrences with up to 42.90% andradite from diverse locations that include Monte Russo di Verra, Italy; Val d'Aosta, Italy; Umba, Tanzania; Passa del Termine, Adamello, Italy; Gunnison County, Colorado, USA; Sierra Tlayacac, Mexico; West Redding, Connecticut, USA; Ala. Piedmont [Italy?]; Salem District, Madras, India; Milendella, South Australia; Luikenlahti, Finland; South Africa (Bushveld and another unspecified location).

Hopefully the above information will be of interest and useful to you.

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PostPosted: Mon Dec 14, 2009 4:04 pm 
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Thank you very much ROM. This information are very usefull for me.

Indeed, it was suprising (to me) to every time eard about grossular-andradite only in Mali.

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PostPosted: Mon Dec 14, 2009 4:23 pm 
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Gemça wrote:

Indeed, it was suprising (to me) to every time eard about grossular-andradite only in Mali.

It was to me as well since the two species have a solid-solution relationship (along with uvarovite) according to Rouse's chart on P. 95. That's why I looked further into the matter. I wonder if uvarovite content in the Mali stones explains the presence of chromium?

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 Post subject: Chrome-bearing Mali Garnet
PostPosted: Tue Dec 15, 2009 9:11 pm 
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Greetings Forum.

The 'normal' color for Mali Garnet, a blend of Grossular and Andradite, ranges from very light greenish-yellow to very dark brown.

There are, however, beautiful green stones found as well which can resemble the finest tsavorite or demantoid. We have tested numerous stones with this strong green color in the past and found that all contained Chromium.

Normally Chrome-bearing Mali Garnet is only found in cabochon or bead quality. In our years of working with 'Chrome Mali' rough, we have been fortunate to get a number of clean faceted gems. The majority of clean faceted Chrome-bearing Mali Garnets weigh 0.30 carats or less.
Only a few have weighed over 1 carat, and one exceptional gem sold last year weighed over 2 carats.

Chrome-bearing Mali Garents are quite rare and truly beautiful gems, resembling, but not looking exactly like Tsavorite or Demantoid. There is no treatment that we know of which has been successfully used to alter the color of Mali Garnet.

Thank you.

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PostPosted: Tue Dec 15, 2009 11:53 pm 
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8) wow, thanks for the info, gemca, ROM, and scott!!

do you have any pics of the chrome-bearing mali garnets that are faceted or rough to post on the forum, scott? would love to see one faceted or a piece of rough. :D


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