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 Post subject: Color Shift in Mali Grossular / Andradite Garnets
PostPosted: Tue Mar 28, 2006 8:52 am 
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Hi Friends!

As I told you I recently puchased a so called "Color Change Dematoid Garnet from Pakistan" That should exhibit a "Color Change from Vivid Olive Green to Flame Orange" last week via Ebay.

I Got the stone (Pear shape 0,63 Cts) Today and found astonishing optical similarities with a selection of Mali Garnets (Grossularia / Andradite mix).

For the Pictures below I photographed a 2,2 Carat Stone from That Collection under Tungsten Light and Osram Coolwhite.

I Take the Purchase of the stone as a lection in "Learning by doing" and am now about to sell off my Mali Material in a proper way.

My Question: I would describe the Material as follows:

Color Shifting Mali Garnet (Grossularite) 2,20 Carats, Heavyli Included
The Material exhibits fair Color shift under different light sources.

Would you agree with that description?

What are your experiences with Mali Garnets?


Greetings from Vienna, AFTER ALL THE SPRING HAS ARRIVED HERE!!!!


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 Post subject: OOOPS! The Pictures here we go...
PostPosted: Tue Mar 28, 2006 9:00 am 
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Tungsten Light Pictures:

Image

Image

Cool White Pictures:

Image

Image


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 Post subject:
PostPosted: Wed Mar 29, 2006 5:33 am 
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Dear Nikolaus,

May be I can help you with what I have seen on "Mali" garnet (grossular with a litle beat of andradite).
This variety of grossular show's an iron band near 440 nm (related to andradite) as shown:
Image
The refractive index can be between 1.760 to OTL (>1.790).
SG can be between 3.57 to 3.72.

Note:
If 3.80> SG > 3.72 you can consider you are in the grossular-andradite part of the grossular <-> andradite serie (andradite > 30% in the mixture)
If SG > 3.80 this is probably andradite (andradite > 70%)

For exemple this green Mali grossular
Image
show the spectrum described above
I have not noted/verified the color change behaviour.
RI= 1.78
SG=3.63
Inclusions:
Generaly heavy included by cracks (1) and/or finger print (2).
(1)Image(2)Image

I will check my Mali grossular with two different light now ;-)

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Jean-Marie Arlabosse
GemInterest.com


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 Post subject: Color Shift
PostPosted: Wed Mar 29, 2006 7:30 am 
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Thanks for the Data Gemca!

I also never looked them up for color shift until two days ago. My guess is that the color shift is related to the mixture percentage of the two main Garnet components Andradite and Grossular since not all my STones show the shift.

Without the puchase of the so called "color change Demantoid" Two weeks ago I would never have had the idea to check them...


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 Post subject:
PostPosted: Thu Mar 30, 2006 3:18 am 
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Seems to me that a number of sellers on a popular online auction site are trying to pass off Mali garnets as demantoids I have noticed an increase in such activity in the passed 3 months. They often say that they are colour change too as if to add value. I am quite a fan of mali garnets but they are not demantoids caveat emptor

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 Post subject:
PostPosted: Thu Mar 30, 2006 7:24 am 
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Isomorph: I also sell off my mali Garnets via Ebay, but I dont call them demantoids - because they are not.

After finding out about the slight color shift, I started to describe them properly as: Mali Garnets (Grossularia Andradite mixture) with slight color shift.

Other sellers (Unfortunately the vast majority it looks like) are just inventing another source (Like Pakistan in case of my purchase) and use the wrong terms demantoid and color change.

Do you have Pics of your Mali garnets? I also like them very much.


Greetings, Nikolaus


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 Post subject:
PostPosted: Thu Mar 30, 2006 11:27 am 
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most gems give a slight colour shift depending on the light source and there seems to be more availability and choice of light sources that one will meet just going to the local mall or shopping center I have also armed myself with a pocket full of different gems has proven this to me (am I sad or what) will post photos soon.
My favourite garnets are as follows
1 Blue garnets colour change
2 Mali garnets yellow green type
3 Spessartine from anywhere
4 Rhodalites from Tanzania
5 Malaya of which colour shift varietys
[/img]

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 Post subject:
PostPosted: Thu Mar 30, 2006 12:09 pm 
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Nikolaus and Isomorph,

This topic interests me. I'm also a Mali garnet fan and have done my best to research them from a chemical/gemological standpoint. As you both probably know, there is not presently a universally recognized system of garnet classification, which makes things enormously difficult.

One fascinating and very rewarding book on the subject is "Naming Gem Garnets" by W.W. Hanneman Ph. d. He's developed what he calls the Hanneman Unified System for Classifying Gem Garnets. It's based on the use of chemical composition to define garnet "mixed species" and/or "end member species." But it's not as yet recognized (or even considered!) by GIA or other gem labs, although it's rooted in the approach taken by the late Basil W. Anderson of Gem-A.

The book contains a wonderful chart (frontispiece) that relates the above information to some of the currently popular "trade names" and/or "color varieties" for various garnets. (It also comes with what he calls a garnet "Rosetta Stone" that delineates garnets by color, R.I. and spectrum, which I've found remarkably helpful in my thinking about this very confusing topic).

With all that exposition I come to the point. Dr. Hanneman says much Mali garnet should be classified as grossular, not grossular-andradite. His chart classifies Mali stones with RI from about 1.733 to about 1.77 as in the grossular range, and those from slightly above 1.77 to about 1.84 classify as grossular-andradite. In his scheme, andradite begins at RI 1.842 and demantoid begins at about 1.867.

I have some questions about the last since everything I've read indicates that demantoid is the green variety of andradite and the distictinction is not based on RI. (I'd have to do some refresher re-reading but I believe he takes the Cr spectrum into account in the demantoid classification but can't recall for certain.) But the Trade's definition of "green" seems to be pretty flexible :lol: with many olive oil-hued stones designated as demantoid. That creates another ruby/pink sapphire-type hue problem, so maybe an RI-based distinction is best.

In any case I look forward to hearing other points of view on the matter. I'm especially interested in the views of others who've read Hanneman's book.

Warm Regards to All,

ROM


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 Post subject:
PostPosted: Thu Mar 30, 2006 2:50 pm 
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I quote:

"Knowledge tells me that a tomato is a fruit
wisdom tells me not to put one in a fruit salad"

Dont know who to attribute that quote to but it seems paticulaly relevant to this topic. in terms of Mali and demantoid garnets, people who buy these stones are usually knowledgable and a seller/jeweller who is honest will inform his clientle. Russian demantiods have the tell tale (Pun not intended) horse tail inclusions and are the exception to the rule that gemstones with less inclusions are more valuable. Demantoids without these inclusions are not considered as valuable or worthy. gem appreciation is not only scientific but very subjective and liable to be influenced by lore, myth and provenance. hence tsavorite garnets whilst being a better bet in terms of colour harrdness and clarity (in my opinion) when compared to emeralds, will probably never reach the cost per caret that emerald do.

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 Post subject:
PostPosted: Thu Mar 30, 2006 3:18 pm 
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Hi Rom and all,

Hanneman puts Mali Garnet in the grossular end of the series due to chemical content and the X-ray diffraction pattern which matches that of grossular.
From what I read, he assumes (if so, correctly in my opinion) that the GIA was unwilling to put them in the grossular classification due to previous established classifications (which they apparently hold in high regard).
Needless to say these classifications were established well before the discorvery of Mali Garnet. A simple correction on the scale would have been sufficient. Instead they put themselves in a tight corner and just named it grossular-andradite: "As a gem variety, we are refering to this material as grossular-andradite, since it lies between two pure end members".
From which Hanneman rightfully concluded: "With this single sentence, they have effectively destroyed the entire garnet classification system."

His article on garnets was never published by the GIA as you mentioned, nor were they willing to review his book "Naming Gem Garnets", which would have helped.

Hanneman's proposed classification based on refractive indices:
Grossular 1.730 - <1.785
Grossular-Andradite 1.785 - <1.880
Andradite >1.880

So Demantoid will fall in the Andradite, according to RI alone.
Mali would fall in Grossular, as logical.

Everytime there is some logic I really can't understand, it usually involves money. There must be a hidden agenda in being persistant in naming Mali "Grossular-Andradite".


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 Post subject:
PostPosted: Thu Mar 30, 2006 3:23 pm 
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isomorph wrote:
horse tail inclusions and are the exception to the rule that gemstones with less inclusions are more valuable. Demantoids without these inclusions are not considered as valuable or worthy. gem appreciation is not only scientific but very subjective and liable to be influenced by lore, myth and provenance.


Speaking of gems made more valuable by inclusions how about rutilated quartz, fine cat's-eye and star gems, nearly all chalcedonies/agates that show dendrites, plumes, fortification banding, moss and many more?

As for demantoids, I buy and sell them so I have a pretty good idea of what adds to and decreases value :) The question in my post is whether all Mali garnets should all be considered grossular-andradites or whether many and perhaps even the majority, are grossulars.

As to subjectivity, lore, myth, etc. I grant your point they are important from the consumer's perspective. But since this forum is devoted to gemology (i.e., literally the scientific study of gems) I felt it was a good place to raise the scientific aspects of this garnet subgroup.

ROM


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 Post subject:
PostPosted: Thu Mar 30, 2006 3:27 pm 
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p.s.: This is what Hanneman wrote to me late last year.
Quote:
Since it has been my considered opinion that the garnet nomenclature system was “essentially ruined” by the system proposed and currently taught by the GIA, I introduced what I considered to be a better one in my book, “Naming Gem Garnets.” In typical fashion, with ideas which are not the product of the GIA, the GIA refused to either review or even acknowledge the existence of this book. Consequently, most of my sales have been to readers outside of the U.S.A.


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 Post subject:
PostPosted: Thu Mar 30, 2006 5:01 pm 
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Thanks Doos. I really do need to review the book but it's marvelous to find someone else who's actually read it!

Yes, the garnet classification system is a disaster not only for the reasons you mention but also for failure to deal with the question of just what constitutes an end-member. GIAs' treatment of 'rhodolite' and 'malaia,' both intermediate mixtures, essentially as species would be funny if it didn't lead to so much confusion.

I've spoken with Hanneman several times on this subject and others and agree that GIA has not covered itself with glory in this matter. If it's truly a scientific organization it should publish papers that run counter to its own orthodoxies. That's especially true when its own research scientists (Stockton and Manson) have published information at great odds with what is being taught in GIA colored stone courses, as Hanneman points out.

If nothing else, this controversy points up the great need for some international protocols to regularize such matters among worldwide gemological organizations. Example: some pink sapphires I purchased in Delhi were graded there as ruby by a CIBJO-authorized lab. I knew what I was buying but the lab reports are useless in the U.S. except to show the stones are natural corundum.

One problem with Hanneman's book is that its very badly organized, with no index. BTW, did you construct his 'garnet refractometer' and learn how to use it? I've struggled with it but can't quite figure out how to make it work. All help is appreciated!

ROM


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 Post subject:
PostPosted: Fri Mar 31, 2006 8:26 am 
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Dear Friends!

It is always a pleasure to see how disussions become a very high level of quality in this forum.

It seems to me unavoidable to read that book that is in the discussion now. If anyone is in posession of a second copy please PM me.

I understand that trading with garnets is a very special case within the gam trade. Many varieties that were now taken into this discussion already went through my hands and over the counter. And, as we see here, still I´m learning new things day by day.

Talking about the demantoids: I strongly disagree with the above stated Opinion that Demantoids would be non precious whren lacking horsetail Inclusions. I have seen and traded Demantoid from various sources. Yes, the king (by price) is and possibly will stay the Russian one with horsetail Inclusion.

But: Do the Russians with their highly saturated green and diffusing Inclusions normally placed beyond the table ever show the amazing Fire and spectral effect that gave these exeptional Garnets their Name?

Demantoids can beat Diamonds in their own game, just as Tsavorites can beat the emeralds.

Truly breathtaking is the sparkle of a fine brilliant cut, and PALE colored Demantoid Garnet. The lack of color leads to a reduced price (Always a good start for a good purchase) in the market, and the lack of color also leads to sparkling rainbows all over the stone.

These Demantoids do actually look and act like green diamonds and can be bought for a penny compared to those.

People do buy them and whenever you put them out in front of a costumer they go WOW!

Are these garnets unprecious because of a lack of Inclusions? With respect, I am not sure that this approach to the demantoids is covering all the aspects of the matter.

The classification of garnets, as I understand so far without having read the book from above, seems to leave many quastions open. Terminology and classification, trade names and Do´s and Dont´s still wait for to be put into a system usable as a foundation for all of them garnet family members.


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 Post subject:
PostPosted: Fri Mar 31, 2006 11:54 am 
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Nikolaus,

Mikon-online sells most of Hanneman's goodies (they are located in Germany) https://sslsites.de/www.mikon-online.co ... d04ab78516

A while ago Hanneman offered me the promotion of the book for USD 10.00 (for USA residents) .. some extra costs and hassle for overseas.
I also negotiated a 30% discount on his other book "guide to affordable gemology" which was good till December last year.

ROM,

I haven't constructed the rosetta yet, but will do so this weekend. Might be fun to give it a try. I'll let you know.
Maybe Dr. Hanneman will do us the honour to join our chats again.


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