gemstone id help needed...

[strmrdr]

I know its impossible to say for sure just from a description but im stumped.

The are in a cameo bracelet that was sent over from france in 1945.
emerald cut aprox. 12mm x5mm
red/maroon with purple undertone.
Slightly double refractive
almost loop clean with an inclusion that looks like a crystal in a diamond looks like at 10x.
Some abrasions on the table and facet junctions.

My first thought was spinel but the double refractive eliminates that.
It has the coloring of some of them Iv seen.

 

[DiamondExpert]

DR would eliminate the garnets too. Impossible to say...tourmaline, a quartz of some sort perhaps????

 

[Richard M.]

No offense intended, but are you familiar with the appearance of anomalous double refraction (ADR)? I have garnets that flicker like a pulsar under the polariscope and hunks of glass that do the same. Using DR to nail down an identification isn't always conclusive. Have you used a dichroscope? Is there any way you can check R.I. and other properties including spectrum?

The inclusion is interesting and it probably indicates (but doesn't prove) natural origin. The stone could be a doublet. In fact, garnet and glass doublets were very popular at the time indicated and that would be my first test. Look at the stone from the side and see if there's any difference in color between the top and bottom halves. If one is colored and the other white it's probably a doublet.

There's a host of other possibilities, natural and not: glass, garnet, spinel, tourmaline, flame-fusion synthetic corundum and spinel (they were invented in France in the 1890s), zircon, andalusite, beryl, quartz, plastics, topaz and probably a few more I can't think of -- even natural alexandrite (unlikely) or its flame-fusion simulant (more likely). If it's important for you to know, take it to a qualified gemologist and pay the small fee to get a professional answer.

 

[strmrdr]

I was looking at it in a higher end resale shop, its way out of my price range.
They have no clue what it is.
When looking thru the table at a pencil line on a white peice of paper thru one of the pavilion facets so it windows and it shows a slight double line.

RI judgeing by the angle it has to tilted to window is likely fairly high expecialy considering the size of the stones.

I dont have any equipment other than a loupe.

She is going to have a local jewler that deals in gemstones look at it.
There isnt a decent appraiser in my area closer than PGS in chicago 70 miles away.

It is the same color and consistancy from top to bottom as far as I can tell.
The lack of zoning, color and the clarity was what had me thinking synthetic spinel.
But DR eliminates that.

No offence taken im a rank beginer when it comes to gemstones with a lot of "book" study but little hands on.

 

[yowahking]

If there is no appraiser in your area, check to see if there is an AGS store, they will usually have a gemologist who can run an RI at least.

 

[DiamondExpert]

"No offense intended, but are you familiar with the appearance of anomalous double refraction (ADR)?"...I think this was in response to my garnet comment, and R.M. you are correct about this potential source of confusion using a polariscope."

No offense taken, and yes, I am familiar with ADR - especially with red/reddish garnets and other high stress synthetics - however, I was taking it as a given that the stone was DR from the first post.

 

[Richard M.]

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On 9/11/2004 1:05:50 PM DiamondExpert wrote:

I think this was in response to my garnet comment, and R.M. you are correct about this potential source of confusion using a polariscope.'

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Ah, the dangers of communicating on the 'net! The comment was aimed at Strmrdr, not you D.E. It wasn't clear to me how DR was established and I thought ADR might be a worthwhile possibility to consider.

Meanwhile, I applaud Strmrdr's approach to practical gemology. Learning to use a loupe effectively and gleaning as much info as possible with it is a great method. Adding a penlight and some Visual Optics knowledge would be another great step. Expensive instruments are always helpful but it's astonishing how much one can do with trained eyeballs, a loupe, a penlight and that marvelous educated 'instrument' located between your ears.

 

[strmrdr]

I did have a penlight with me but there was strong sunlight coming thru a window that was perfect for looking at gemstones.

Can you clarify what you mean by "Visual Optics knowledge" and give me some specifics on what to study?

My formal training in optics was with lasers and 14 years ago.

 

[Richard M.]

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On 9/12/2004 12:13:42 AM strmrdr wrote:

Can you clarify what you mean by 'Visual Optics knowledge' and give me some specifics on what to study?

.
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Visual Optics (aka The Hodgkinson Method) isn't too well known yet but it's powerful. It was pioneered by Scotsman Alan Hodgkinson F.G.A. who happened to look at a street light through the table of some gems he had in his pocket one night (he was driving cab in Edinburgh to support his gemological studies).

He noticed that patterns of the refracted streetlight appeared differently from stone to stone: low R.I. stones showed a pattern of lights in a small cluster while higher R.I. gems show a much wider pattern. He also noticed that small spectra were also visible: single patterns for singly refractive stones and double patterns for DR stones. While this information was not new, it remained to Hodgkinson and his American associate William Hanneman Ph.d to develop it into a usable system for virtually instrument-free gem identification. (Of course a knowledge of gemology and what all those clues mean is essential).

It takes a lot of practice but is fairly simple once the fundamentals are understood. Using VO it's easy to quickly sort out diamonds from moissanite and CZ and vise-versa using just a penlight, tweezers and your trained eyeball. Separating garnets from rubies is child's play, as are many other colored stone determinations. It doesn't replace gemological instruments for complicated IDs but it's indispensable when buying where no instruments are easily available.

A good discussion can be found at: Visual Gemology

 

[strmrdr]

kewl thanks for the link :}

 

[Richard M.]

The link just gives a general idea of what VO accomplishes and the writer doesn't follow the Hodgkinson approach (although he makes some very interesting points). I'm going to build one of his little VAD gizmos next week.

Both Hodgkinson and Hanneman have published what amount to "textbooks" for their approach, complete with photographs and sketches. Hanneman has also developed what he calls a "Birefringence/Dispersion Ratio Index" (aka B Ratio) which (with practice!) is very useful.

Hanneman Gemological sells a lot of the books and papers very reasonably. (No connection, I just found them useful when studying VO). You can get a catalog by writing the company at P.O. Box 1944, Granbury TX 76048.

 

[mhread]

did you think of Zircon? The colour you describe (red/maroon) is rare in zircon, but can be found commonly in two locations. kisawani (Africa) material has that exact colour you describe, and Harts range (Northern Queensland - Australia) does too, but tends often to have copper pink colour. I have also seen Indian red/maroon material, and also some Nepalese od this colour.

Zircon also has the high RI and is also DR. Just a thought.

Martin

 

[strmrdr]

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On 9/28/2004 3:59:44 AM mhread wrote:

did you think of Zircon? The colour you describe (red/maroon) is rare in zircon, but can be found commonly in two locations. kisawani (Africa) material has that exact colour you describe, and Harts range (Northern Queensland - Australia) does too, but tends often to have copper pink colour. I have also seen Indian red/maroon material, and also some Nepalese od this colour.


Zircon also has the high RI and is also DR. Just a thought.


Martin

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hmm interesting.
I will be stopping in this week and will ask her if she found out anything more about it.
I wouldnt have even thought of zircon.
The zircon Iv seen has the sorta glassy/diamond look off the surface in bright floresencent light where this is more of a "gemmy" look.
ie the facets dont act as much as surface mirrors, less surface reflections than diamond.
If I had the money id be real tempted to buy it just to find out for sure what it is lol.

 

[Richard Sherwood]

Hi Storm. There's a topic under the Guerilla Gemology forum with photos and a in-depth description of Alan Hodgkinson's "Visual Optics" system. Fun stuff.

The first thing that came to my mind from your description was synthetic sapphire. Do they resemble amethysts, with purplish or bluish overtones in different lighting?

 

[strmrdr]

thanks Richard I will look into it.
The color isn’t like any synthetic sapphire I have seen but it’s possible.
With its age it might be some that isn’t commonly made any more.
Iv looked at it under a desk lamp, florescent and daylight I didn’t notice a color shift or undertones other than the light purple.


It is likely I will never know :{
She isn’t interested in finding out if it involves spending money and it’s out of my price range.

 

[mogok]

Well red brown zircon can also be found in Mogok, Burma and I've seen one or 2 also in Cambodia recently. Red zircon owns its color to the action of the uranium contained inside the stone (not enough to make the stone dangerous) that will slowly destroy the crystal structure of the zircon. The zircon crystal will then grow and go from high to low zircon. The volume of the stone expend, the RI get lower and the doubling or the birefringeance also get smaller as the stone is getting more amorphous. Zircon is still britlle so it get easily some abbrasion (did you said the stone was presenting some abraded facet jonctions?)
Well it does not identify the stone, but I remember to have failed one of my first gemology test in Burma while studying there with one of these metamict red zircons!

All the best,

 

[mhread]

Mogok - you failed one of your first gemmology tests? Surely not! I could not imagine that.

Red and brown/red appears fairly commonly, and I have much in my collection from all over. I have not seen any of the burmese material you mention. But I am thinking more of the maroon/purple material. This colour is not found commonly outside the two locations I mentioned in my previous post. If you have any, I would be more than interested in getting hold of some, with a preference for rough if possible.