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PostPosted: Tue Mar 06, 2007 4:35 pm 
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Thanks so much, Gemça.
That's just what we needed to know.
Indeed the absorption band around 430-440 is the result of manganese, and the total absorption thru the violet is the result of iron.
Here are two spessartite spectrums Gemça sent me privately:
The following represents your typical spessartine spectrum:
Image

As additional iron substitutes for the Mn, and you approach a spessartine/almandine mixture, the spectrum will look like this:
Image


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PostPosted: Tue Mar 06, 2007 4:41 pm 
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Thank you! What a wonderful resource! Bookmarked.

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PostPosted: Wed Mar 07, 2007 2:12 am 
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Thank you barbra, rom

In fact Mn2+ give equally a partial absoprtion of the violet (plus strong bands at 410, 420, 430..) and some time iron (Fe2+) can help /complete this partial absorption of violet if mixed in spessartite.

Iy you have a strong mixture of spessartite-almandin (i.e. Mn2+ + Fe2+) the spectrum can look like this:
Image
Or even more absorbed!

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PostPosted: Sat Apr 21, 2007 11:15 am 
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I was playing around with the spectrascope looking at some rough garnets. I have a small parcel of Malaya's that I recently bought and all the spectras were pretty similar except for this one stone. This one has very sharp but a bit faint lines at 6500, 5800, 5650, 5400, 5200 and gereral absorbtion from 4000 to 4200.
I haven't observered a garnet before with such a thin sharp line, usually they are much broader and softer like the images above from Gemca.

Has anyone else seen such lines in a garnet? Thinking maybe ROM, Gemca or Barbra may have some experiance here.

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PostPosted: Mon Apr 23, 2007 3:36 pm 
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I like to rebember you some articles about the classification of the garnets in previous issues of Gems & Gemology Winter 1982 p. 204ff, Spring 1983 p. 37ff and certainly the issue Winter 1985 p.205ff.

I used the proposed classification written by Carol M. Stockton and D. Vincent Manson in my book 'Tables of Gemstone Identification".

This classification was and is the most easiest to identify the different garnet members.

Hi Barbra you can try out your garnets with Table 7 in my book.

The students in our belgian gemological schools use the classification for identification of the garnets without any problems.

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PostPosted: Mon Apr 23, 2007 5:32 pm 
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Precision Gem wrote:
I have a small parcel of Malaya's that I recently bought and all the spectras were pretty similar except for this one stone. This one has very sharp but a bit faint lines at 6500, 5800, 5650, 5400, 5200 and gereral absorbtion from 4000 to 4200..


Too busy today to research this in detail, but remember: Malaia/"Malaya" is mainly a mixture of two SPECIES, pyrope and spessartine. It can also contain significant quantites of other species, typically almandine, andradite, grossular, uvarovite and goldmanite.

So depending on the quantities of each, you may be seeing quite a mix of spectra. Typical Malaia spectra have manganese lines at 412 and 432 according to information I have at hand.

Much garnet is sold as "Malaia" that isn't. In fact, I'm not really sure what it is myself because its properties are pretty arbitrary, depending on whom your "authority" is. Sounds like you're having fun though!

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PostPosted: Wed Oct 31, 2007 9:25 pm 
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So garnets are very much like oak trees - they can create "new" species by combining.

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PostPosted: Tue Jan 15, 2008 2:52 am 
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ROM, what's goldmanite?


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PostPosted: Tue Jan 15, 2008 3:26 am 
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gingerkid wrote:
ROM, what's goldmanite?

It's one of about 25 or so garnet species -- like grossular, almandine, spessartite, etc. Only 5 garnet species (6 if you count uvarovite) are used as gems but other species like goldmanite often make up small percentages of the gem garnets.

In the morning I'll post more info on goldmanite as well as some of the other species in the large garnet group.

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PostPosted: Tue Jan 15, 2008 2:54 pm 
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gingerkid,
Garnets are classified by chemistry, i.e., andradite is a calcium-iron garnet species; grossular is calcium-aluminum, and uvarovite is calcium-chromium.

Goldmanite is a calcium-vanadium garnet species but doesn't occur in crystals large enough for gem use although it (along with other minor garnet species) often is present in gem garnets.

Other calcium garnets include species like kimzeyite, hydrogrossular and hydroandradite.

Minor manganese garnet species include yamatoite, calderite and blythite, for instance. There are minor species in magnesium, iron and yttrium garnets as well -- and I've probably left some types out. Over 20 species are presently known and mineralogists say many more are possible.

The gem garnet species are almandine, pyrope, spessartite, grossular and andradite. Some would include uvarovite, which is used as crystalline druses in jewelry. Garnet mixtures, like pyrope-almandine and pyrope-spessartite are given color variety names like Rhodolite and Malaia/Malaya, etc. Of course marketing names for individual garnet colors abound: grape garnet, umbalite, imperial, mandarine, fanta, etc.

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