What is the criterion required for a Green Grossular garnet to be a Tsavorite??

[Vismay Zaveri]

I have Rough of Green grossular garnet from Africa. I wanted to know what is the criterion to name a green grossular as a Tsavorite as chemically and ideally they are the same thing.Is the chromium content the issue.I have a picture of my Green grossular and it shows good fire.
Please tell why it can/can''t be sold as a Tsavorite.Any info shall be greatly appreciated.
Thanks

 

[Pandora II]

Date: 8/4/2008 4:01:35 PM
Author:Vismay Zaveri
I have Rough of Green grossular garnet from Africa. I wanted to know what is the criterion to name a green grossular as a Tsavorite as chemically and ideally they are the same thing.Is the chromium content the issue.I have a picture of my Green grossular and it shows good fire.
Please tell why it can/can't be sold as a Tsavorite.Any info shall be greatly appreciated.
Thanks

Tsavorite is a variety of green grossular. Not all tsavorite has chromium, some are coloured with vanadium.

I would guess that your stone is a grossular/andradite mix (grandite) which is why you will be getting good fire. What is the RI? Tsavorite is 1.74 - I'm guessing your stone will be nearer to 1.77.

I have a mali garnet which has extremely good fire, but my tsavorite is very different in character. Both are varieties of grossular, but one has the addition of andradite. Demantoid is the best known of the andradite garnets - hence the high dispersion that that stone has.

I am finding that 'pure' breed garnets are very hard to get hold of. The isomorphic replacement found in garnets makes each stone a new guessing game as to exactly what proportion of what is in something.

To be honest it's not really a good enough colour to command much of a price as a tsavorite. It would be a good colour in a demantoid though!

Any more info on the stone? Where did you get it? Do you have the SG or the RI?

 

[Proteus]

According to GIA, the color range for tsavorite is medium-light to dark tones, with hues ranging from green to yellowish green. I think typically it''s just called green grossular or mint garnet if it''s light in tone. It''s similar to how a light-toned emerald should technically be called "green beryl."

Though judging by the photo, I would agree with Pandora that it could be a Mali garnet. It appears to have a yellowish-green hue, which is more typical of Mali garnets (though not impossible for grossularite.) If you can get an RI or any other gemological data, that would help determine exactly what it is.

 

[Richard M.]

There is no generally agreed-upon color standard. It''s subjective, like the old ruby vs. pink sapphire dilemma where the time-worn joke goes: it''s ruby if you''re selling and sapphire if you''re buying.

While GIA may set some arbitrary color parameters, GIA does not yet rule the entire gemological world and there''s a lot of disagreement on such color distinctions. The Gem Guide, which tracks gem prices, describes Tsavorite as "Very strongly bluish green, bluish green, very slightly bluish green, green, slightly yellowish green, yellowish green and strongly yellowish green.

It says "extremely light" tones are more properly classified as green grossularite (MintGarnet, Merelani Mint and a few other names in the gem Trade).

Richard M.

 

[Proteus]

GIA''s color grading is not necessarily arbitrary, especially when you consider laboratory analysis. Their standards are an attempt at a scientific method of describing gemstones, and in a laboratory environment, you need a certain amount of scientific protocol. Most gemological laboratories will tend to follow (at least loosely) GIA''s standards. Color grading is always under debate, as it all boils down to opinion, and opinion is always subject to human error. Thus there will always be arguments about the color of a diamond or colored gem. But, it doesn''t hurt to err on the side of caution... you can always take a stab in the dark when you decide what to call a gem, but that can come back to bite you later. Especially if you sell a gem as a particular variety, and your customer decides to have it verified by an independent laboratory, and they say it''s not what you sold it as. That could get you into a lot of trouble. Granted this will probably only be an issue with more expensive gems, but you never know.

GIA certainly doesn''t rule the gemological universe, they just happen to be a common source of gemological standards. You don''t have to like them, but you will probably run into their standards quite often, so you might as well be familiar with them.

GemeWizard is a pretty common method of communicating color these days. There is a free version on their website which you can use to help you decide what hue, tone and saturation a gem is. There will be some discrepancy due to monitor color calibration, etc. but it''s a good estimate and a good place to start.

 

[Richard M.]

Tony, I think you misread my comments. For anyone, not just GIA, to decide when a tsavorite color becomes mint (or pink sapphire becomes ruby) is an arbitrary decision. Someone must create an arbitrary point beyond which a color goes by a different name. After all, pink is really a shade of red and mint-color is a shade of green.

I wasn''t being antagonistic toward GIA. Sometime back someone here posted GIA''s color parameters for distinguishing Tsavorite from mint. Well and good. It''s still an arbitrary distinction and my point is that not everyone in the world agrees with it. When I have pink sapphires graded by labs in Sri Lanka or India they''re called rubies. I think it would be lots simpler if all red hues of corundum were called ruby, and all green hues of grossular were called tsavorite. But I don''t make the rules and I''m not sure who does!

 

[Proteus]

Richard, thanks for clearing that up. I understand exactly what you meant now.
Yes, there is always that ugly "gray area" for what a gem should be, and who really has the right to decide anyway? It''s all up to personal taste in the end.
I just wanted to point out that if you''re really uncomfortable with deciding on what to call something, sending it to a major lab can be worth it -- the gem lab will be the responsible party for stating the variety, which takes the heat off of yourself!

They have a reputation, so people will tend to believe in them, as it''s a third-party professional opinion. That doesn''t mean they''re always right, though.

 

[RevolutionGems]

One thing I haven''t seen mentioned here is place of origin. Tsavorites are named for their place of origin, Tsavo national Park. It is like calling a Moz tourmaline a Paraiba. Technically, only garnets from that one area are true Tsavs or Mints while other that look similar are only look-alikes.

I think in this case, the value is being placed on the name of the stone as opposed to the stone itself. Can it be sold as a Tsav? Maybe, but you would have to reference all the information mentioned in the other post regarding RI and chemical content, etc.

My personal belief is that unless it orginated from the Tsavo Park, it should not be sold as Tsav. just as Moz or Nig tourmaline should not be sold as Paraiba.

Simply my 2 cents worth...

 

[Pandora II]

Date: 8/5/2008 2:13:03 PM
Author: Revolution
One thing I haven''t seen mentioned here is place of origin. Tsavorites are named for their place of origin, Tsavo national Park. It is like calling a Moz tourmaline a Paraiba. Technically, only garnets from that one area are true Tsavs or Mints while other that look similar are only look-alikes.

I think in this case, the value is being placed on the name of the stone as opposed to the stone itself. Can it be sold as a Tsav? Maybe, but you would have to reference all the information mentioned in the other post regarding RI and chemical content, etc.

My personal belief is that unless it orginated from the Tsavo Park, it should not be sold as Tsav. just as Moz or Nig tourmaline should not be sold as Paraiba.

Simply my 2 cents worth...

Hmm, didn''t Campbell Bridges find tsavorite in Tanzania to begin with, but due to export problems he went hunting for it in Kenya and found it in the Tsavo National Park. I know Tiffany named it, but I always wondered if Mr Bridges would apply the same name to the product of his original find?

I''m totally with you on the Mozambique cuprian elbaites.

One quick question - my understanding was that ''origin'' was the term for the genesis of a gemstone rather than its place of finding and that should be referred to as ''locality''. Yet everywhere I look - bar the Gem-A course notes - origin is used for location. Thoughts - pedant that I am????

Tsavorite is a hard one as well because it''s not an actual species in itself like Spessartite is.

Is tsavorite a ''pure'' form of grossular, or is it like so many of the other garnets in that it may have differing proportions of other types? If it isn''t a pure form, where does tsavorite begin and end?

Did anyone go to the Garnet Symposium earlier this year?

 

[RevolutionGems]

Pandora,

Again, you amaze me! I know I hooked up with you for a reason

You are, of course, correct. I should have said locality. I can''t answer the question of species purit but, from what I have heard, there are no "pure" garnet species. Evry one is, to some degree, a mixture of two or more species.

I love this! It just brings to light one of the true beauties of garnets. Infinite possiblilities, so much variation, so much beauty.

Plus, name one other stone that features both some of the cheapest AND some of the most expensive stones available.

Gotta love it!

 

[Vismay Zaveri]

Thanks for the Reply, It is indeed a mali garnet (Grandite), It has an RI of 1.78, and i have tested it for specefic gravity but dont have record as of now.I even had the chemical analysis done and it showed the presence of both calcium and iron along with aluminium (As one would expect).Besides this i have got Garnets of Bottle green colour from the same Area.

 

[Pandora II]

Date: 8/5/2008 2:34:13 PM
Author: Revolution
Pandora,

Again, you amaze me! I know I hooked up with you for a reason

You are, of course, correct. I should have said locality. I can''t answer the question of species purit but, from what I have heard, there are no ''pure'' garnet species. Evry one is, to some degree, a mixture of two or more species.

I love this! It just brings to light one of the true beauties of garnets. Infinite possiblilities, so much variation, so much beauty.

Plus, name one other stone that features both some of the cheapest AND some of the most expensive stones available.

Gotta love it!

LOL, I''m glad you love it, it drives me nuts!

Oh, on the origin thing, it wasn''t aimed at your comment, I was looking for generally thoughts on usage...

Garnets, definitely the second great love of my life - after my husband of course.

 

[Pandora II]

Date: 8/5/2008 3:52:34 PM
Author: Vismay Zaveri
Thanks for the Reply, It is indeed a mali garnet (Grandite), It has an RI of 1.78, and i have tested it for specefic gravity but dont have record as of now.I even had the chemical analysis done and it showed the presence of both calcium and iron along with aluminium (As one would expect).Besides this i have got Garnets of Bottle green colour from the same Area.

Thanks for coming back to let us know!

I am a new convert to Mali's. I just bought one from ArtCutGems and I have been carrying it around with me since it arrived so I can look at it in loads of different lights. Better than a diamond in my mind! Here's a photo that doesn't begin to show the dispersion or the amazing colour shifts (yellow/green in daylight with orange flashes and orangeybrown in incandescent light)

The stone in my avatar is a tsavorite.

You have garnets... where are the photos. You can't come here telling us about rocks that you have without pictures!

 

[Pandora II]

Ooops forgot to attach pic - photo by the vendor.

 

[RevolutionGems]

OWWW! Remove the dagger from my heart!

But seriously, you just got married recently, no?

 

[Pandora II]

Date: 8/5/2008 4:28:10 PM
Author: Revolution
OWWW! Remove the dagger from my heart!

But seriously, you just got married recently, no?

Aw, now I feel bad!

I got married on the 26th July.

 

[Harriet]

Date: 8/5/2008 2:23:31 PM
Author: Pandora II

Is tsavorite a ''pure'' form of grossular, or is it like so many of the other garnets in that it may have differing proportions of other types?

Yes, so I''ve been told.

 

[marcy]

Pandora, congratulations on your recent marriage. I too love to read your words of wisdom. I was just searching around my self on the grossular mint garnets I bought to see where they fall in the world of garnets.

 

[Richard M.]

Hi Pandora,

I didn''t go to the Garnet Symposium. I''m sorry I missed a couple of presentations but much was a re-hash of stuff I''ve already studied pretty thoroughly.

The ''pure'' form of grossular is colorless. Grossular has the widest color range of any garnet species, with natural stones ranging from colorless through green shades, yellows, orange and brownish orange (the hessonite variety). As you yourself pointed out in this thread, green grossular is characterized by the presence of chromium, vanadium or both. My research indicates vanadium is primarily responsible for tsavorite''s green hue.

Quite a number of colorless Tanzanian grossulars have been found as well as yellow and golden ones (described in "Colorless and Green Grossularite From Tanzania," Gems & Gemology, Summer 1979). Colorless ''pure'' grossular has the chemical forumla: Ca3 Al2 (Si)4)3, or three calcium atoms, two aluminum atoms and three silicon atoms for every 12 oxygen atoms. Its RI is in the 1.732-1.736 range. (Color is determined by the presence and amounts of trace elements).

Since that article was written the deposits in Mali, West Africa, have yielded a large number of stones that are basically grossular, some with enough andradite content to be called "grandites." Most are technically grossulars but when the R.I. exceeds 1.77, according to my garnet guru, Dr. William Hanneman, they join the grossular-andradite series (grandite).

There is great professional disagreement about how garnets should be classified. Dr. Hanneman''s method makes the most sense to me but it''s at odds with GIA and several other authorities including Gem-A, I think (even though Hanneman''s approach is based on Gem-A work by Basil Anderson -- it''s all very confusing). For a good discussion of the problem see Hanneman''s book "Naming Gem Garnets."

 

[Sagebrush]

Richard, et al.

I did not attend the garnet symposium. Have you read the Stockton Manson article in Gems & Gemology (winter 85) A Proposed New Classification for Gem Quality Garnets?

Seems like a system based on RI would be superior to the current system.

 

[Richard M.]

Hi Richard,

Welcome back. Yes, the Stockton-Manson research is very much in harmony with Hanneman''s classification system. I have all the articles on file and refer to them often. Hanneman''s Rosetta Stone of Garnets determines species/color variety based on R.I., color and spectrum. S.G. is notoriously unreliable due to error-causing inclusions.

Richard M.

 

[Sagebrush]

Richard,

The recent description in G&G (Summer 2008, p.166) of the spessartite garnets from the new strike at Lindi, Tanzania is kind of amusing.

The garnets are described as almandine-spessartine, with minor pyrope and grossular componants. The writer (Elisabeth Darenius) notes that slightly lower RI and SG is "most likely attributable to the minor pyrope and/or grossular components."

So I guess that makes them almandine-spessartiine-pyrope-grossular garnets. What''s left? I am not familiar with the source you site but maybe its time for a new system.

 

[Richard M.]

Richard W.

Without getting into all sorts of complexities like isomorphous replacement, miscibility and solid solution end-members, let me say that you''ve pointed out the biggest problem in garnet ID/classification.

Garnet species are very prone to mix with one another in varying percentages. There''s no universal agreement about when any specific garnet contains enough of any particular species to be called by that name (almandine, spessartite, pyrope, etc.) GIA has one set of rules, mineralogists another, and gemologists don''t really give a damn because they depend on varietal "color names" like "grape," "Mandarin," "rhodolite," "malaya/malaia," "Imperial," "Tsavorite," etc. to sell garnets.

The goals of mineralogists, who are obsessed with classifying everything by chemistry and naming minerals after discoverers or their buddies or financial benefactors, are very different than gem merchants. Gem merchants simply want to enjoy and sell pretty stones. Neither they nor their customers give a gold-gilded hoot about the intricate chemistry of their merchandise or its proper mineralogical classification. Color, quality and price are far more important.

Dr. Hanneman has proposed a compromise. It''s a system that recognizes the gem merchant''s needs while also adhering to strict gemological and mineralogical guidelines. It''s based on Stockton & Manson''s studies but makes room for commercial needs. It makes sense to me, a gem merchant, and it has the added advantage of being quite easily understandable. Problem: GIA won''t acknowledge it exists.

Richard M.