January 24 Through February 4—TUCSON, ARIZONA: Annual show
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PostPosted: Mon Mar 05, 2007 12:07 pm 
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So far MoDo has 99.97%, I changed #3 to rhodolite, her 2nd choice.
More garnets will follow later today.
#1: Spessartite
#2: Grossular (Tsavorite)
#3: RHODOLITE from the absorption spectra
#4: Grossular (Tsavorite) The one I want!!!
#5: Spessartite
#6: Color-change (Pyrope-spessartite mixture)

If anyone has any interesting garnets to add, please post them! :smt064
Precision Gem??? Are you feeling a little nudged?

I'll go back and add all these photos to their proper spot in the original post when I finish getting the specs on them.


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PostPosted: Mon Mar 05, 2007 2:04 pm 
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Garnets are one of my favorite stones to work with. You have my interest here. Just last night I assembled a gem box with 10 garnets of various types. Rhodolite, Umbalite, Malaya, Colorchange, Spesspartite, Mali, Mint Grossularite.

I'll try to cut into my cutting time, and post pictures and measurements. My German refractometer only came with RI fluid good to 1.79, I guess it's a European law, so my measurements will end there.

Betweem this forum and American Idol, I'm not getting any stones cut lately!

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PostPosted: Mon Mar 05, 2007 3:03 pm 
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ROM wrote:
Hi All,
I'm proud of color-changers in my inventory too. I have lots more, as yet not photographed. These are all pyrope-spessartines from Tanzania. From top to bottom they are: 1.5 ct., 1.18 ct. and .53 ct.

Image

Image

Image


Some of the pyrope/spessartines do a lovely dance from purple to raspberry, others are seriously rock and rollin', approaching a fine alexandrite's green to raspberry. What do you think is responsible for the difference?
PS. I love your photos. Are you doing that on a mirror, or highly reflective surface?
Also have you rigged up an incandescent /daylight light source to snap these shots?
Stellar!


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PostPosted: Mon Mar 05, 2007 3:09 pm 
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Precision Gem wrote:
Cut of the day...
This is one of the Kenyan color change garnets. These are real pictures, not 1 picture photoshopped to look like a color change. This stone is brighter than most of the color change garnets I have had. Not too much of this around the past year. The guy in Kenya I get my rough from usually has about 20 of these stone per year, this year he only had 2.

2.54 cts.

Image
Incadescant Light
Image
Florescent light

PG, Are you photoshopping the attractive draped backgrond behind your shots?


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PostPosted: Mon Mar 05, 2007 3:34 pm 
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Example 7

Image
We'll just refer to this gem as, "WOW".
Carat weight: 22.80 cts.
Specific Gravity: 4.22 (a little higher than normal for spessartite, wonder why :? )
RI:Over My limit of 1.81
Spectroscope:
Image
We see a lot more absorption due to iron here in the blue part of the spectrum. This could also account for the increase in SG.
Microscope: More very fine needles:
Image

I think this could be described as an almandite/spessartite mix.
Comments?


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PostPosted: Mon Mar 05, 2007 3:45 pm 
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Barbra Voltaire wrote:
Some of the pyrope/spessartines do a lovely dance from purple to raspberry, others are seriously rock and rollin', approaching a fine alexandrite's green to raspberry. What do you think is responsible for the difference?
PS. I love your photos. Are you doing that on a mirror, or highly reflective surface?
Also have you rigged up an incandescent /daylight light source to snap these shots?
Stellar!

I have no real evidence to support the difference unless chromium is involved, as it usually is in that combo. Vanadium is frequently mentioned as the cause of the color change in pyrospessartites but I can't recall any specific research on this. No time today to dig out Manson & Stockton's writings on the subject. Garnets exist in many other color change combinations as well. It seems like a great research project for someone.

As for my images, yes and yes. These were shot on a mirror with interchangeable lighting from approx 3500 K. to 5500 K. But the colors shown are only accurate for those specific lighting conditions. The colors will change enormously in mixed light, direct daylight or the variety of lighting conditions encountered during a day's wear.

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PostPosted: Mon Mar 05, 2007 4:30 pm 
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Barb, actually the background on my pictures is a clear plastic gem stand. It's a little thing I picked up a few years ago at one of the display vendors in Tucson. The stand is made of two cylindrical clear plastic rods attached at each end to a clear plastic leg. The rods are spaced about 1/8" apart, so that the craddle a stone pretty well. The only stones that don't work well on them are trillion cut. On the picture above, the stone was not sitting totally in line with the rods, so they look like they are at an angle. I always crop the images and rotate them.

My whole set up is pretty simple. I use a cloud dome, an overhead shop florescent light, and 2 Solux lights with goose necks that I wiggle around. For the florescent shot of the stone I turned off the Solux bulbs, and brought in a small florescent desk lamp I have. Just shined that on one side of the Cloud Dome to add to the over head lighting.

I then do a white balance adjustment inside the Cloud dome on a white piece of paper, then shoot away.

The Cloud dome works well, but I do loose sparkle and dispersion. I have been thinking of drilling a bunch of small holes into the dome. But I hate to mess it up since the darn thing cost sooooo much. I really think you could do the same thing with a big white tupper wear bowl from Walmart for about $6.99. Maybe some LED's inside the dome would help too.

Between a full time engineering job, cutting, building the website, buying rough, playing with the spectroscope, I just don't have a lot of time to work on the pictures.

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PostPosted: Mon Mar 05, 2007 7:12 pm 
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All right ... I'm going to attempt to show one of my spessartite garnets. The photo is from my scanner so not the greatest.

Image


The stone is actually completely bright orange ... there is no brown. Wish I knew how to take close-up shots with a digital camera :P . Hmm ... I expected a thumbnail photo :? . Well, heck ... at least I got this far! :P

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PostPosted: Mon Mar 05, 2007 7:20 pm 
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MoDo,
Try the "Direct" URL at ImageShack. The image will show up in your Preview panel before you post, so you can tell if you did it right.

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PostPosted: Mon Mar 05, 2007 8:14 pm 
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Thanks, Rick ... I'll give it a try next time :D .

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PostPosted: Mon Mar 05, 2007 8:46 pm 
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Ok, THe color change I cut posted above measures:

RI = 1.751
Spectra: General absorbtion from 4000-4400 Bands at 5100 a very thin band at 5325 and a band at 5800

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PostPosted: Mon Mar 05, 2007 11:25 pm 
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An attempt at the spectra

Image

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PostPosted: Tue Mar 06, 2007 12:02 am 
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Barbra Voltaire wrote:
Example 7

Spectroscope:
Image
We see a lot more absorption due to iron here in the blue part of the spectrum. This could also account for the increase in SG.

I think this could be described as an almandite/spessartite mix.
Comments?


I agree with your ID but could the line in the blue be manganese -- the spessartite signature -- not iron? [Anderson & Payne, page 181.] Or are you referring to the cutoff at the far right?

As for the s.g., ferrous iron from the almandite could easily account for it but I'm not entirely sure how it would affect the spectrum. Hanneman believes s.g. is immaterial in garnet ID because it can vary greatly due to isomorphous replacement and isn't a reliable indicator. But his method involves knowing the R.I. which is the Catch 22 unless you can figure out how to use his pinhole Garnet Refractometer -- a feat that escapes me. I think I understand the principle but it never seems to work out in practice.

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PostPosted: Tue Mar 06, 2007 10:16 am 
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Quote:
line in the blue be manganese -- the spessartite signature -- not iron

I was referring to the total blacking out from the blue thru the violet.
But checking with www.geminterest.com I was trying to find out of there is an expected absorpsion for Mn2 or Mn3. I don't find it?
Anyone?


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PostPosted: Tue Mar 06, 2007 4:26 pm 
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Hello all,

In the www.geminterest.com spectrum rubric, the litsting is baddly classed. Sorry.
I have done the mistake to class sepssartite at "grenat spessartite" :?
So,
go to
http://www.geminterest.com/spectlist.php?lettre=G
scroll down to "grenat spessartite" check boxes then click on a "OK" button.
You will be able to see spessartite spectrum in a new windows.

more directly: http://www.geminterest.com/spectlistpop.php?&IDcheck[]=103&&IDcheck[]=101&&IDcheck[]=102&&IDcheck[]=61&

You will see that manganèse (Mn2+) in deformed cubic coordiantion in the spessartite garnet is responsible for the 410, 420, 430 nm and 460. 480 nm absorption bands.
the three bands near 410, 420, 430 nm often merge to furnish a cutoff near 430nm and some time to 440 nm.

In other world: Mn2+ is responsible of the big absorption in the bleu..

But you can aslo have some Iron mixed in the spessartite (i.e. almadine mixed with spessartine) that can give extra bands at 460, 500, 525 and 575 nm and partial absorption in the violet to blue part.
Thus Iron can also be responsible to the darkness of the blue part of the spectrum :wink: .

Hopa that help

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