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 Post subject: Looks like Aquamarine
PostPosted: Wed Jan 30, 2008 10:39 am 
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Could someone help me identify a gemstone that looks like a swimming pool blue aquamarine (exactly) but has a measured RI of 1.50 and a specific gravity of around 2.50. This is not a good picture, the stone is brighter and more silvery than the pic shows. I'm stumped.

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 Post subject:
PostPosted: Wed Jan 30, 2008 11:00 am 
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Have you checked to see if it is doubly refractive or not? Could be glass if it in singly refractive and your other test results being accurate.


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 Post subject:
PostPosted: Wed Jan 30, 2008 11:12 am 
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Carrie wrote:
Have you checked to see if it is doubly refractive or not? Could be glass if it in singly refractive and your other test results being accurate.


It is not doubly refractive. In fact, on my RI meter, it is steady at 1.50 when you rotate the polarizer but there is a strange prism effect showing up below 1.50.

I was thinking it could be glass....the thing is, it doesn't look like glass. Sitting next to a true madagascar aqua it looks nearly identical except maybe a little better with a lot of brilliance and silvery flashes. It also has what look like aqua typical linear growth tubes and a fingerprint inclusion under the 30x loupe.

Is there any simple way to confirm or rule out glass?


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 Post subject:
PostPosted: Wed Jan 30, 2008 11:26 am 
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What you have done with the refractive index is positively rule out aqua.
There are not many possibilites for a singly refractive stone with an RI of 1.50 and SG of 2.50
Actually, looking at the GLASS table in Dedeyne's Tables of Gemstone Identification it is corresponding to what one would expect for glass.

Perhaps you are misinterpreting the nature of the inclusions.
Also check for any small conchoidal fractures on the stone.
Glass is often warm to the touch. If you put a stone on your forehead it feels cool. When you put a piece of glass on your forehead it feels room temperature.

There is also the Dick Hughes hair test. Wrap a piece of hair around the stone. If it's glass the hair will burn when you try to ignite it with a match, if it is a stone it will not. That stems from a quick test to tell the difference between a jade bangle and an imitation glass bangle in Burma.


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 Post subject:
PostPosted: Wed Jan 30, 2008 11:39 am 
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Do you not have a regular refractometer? (I ask cause you said RI "meter") If you do, test the stone for its RI rotating it 30 degrees or so each time till you get the absolute highest and lowest reading. Some stones can appear SR is one direction and DR in another. Do you have a polariscope?

If you feel sure it is SR, characteristics we look for in glass are:
-warm to the touch
-bubbles
-rounded facet junctions or concave facets
-orange peel or wavy texture
-swirls
-conchoidal fracture
-strain colors and strong ADR common

Sometimes you won't see any of that on glass though. Sometimes you just have a stone that is SR and the RI or SG is not appropriate for what it looks like. And with that low RI, you always have to suspect glass.


Last edited by Carrie on Wed Jan 30, 2008 12:03 pm, edited 1 time in total.

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 Post subject:
PostPosted: Wed Jan 30, 2008 12:02 pm 
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Hi cutter,
My lab manual also says this about the properties of glass:

Magnification:
Flow lines (swirls striae), gas bubbles (spherical, oval, elongated, tubular, may be drawn out and appear to have "tails").....

Fluorescence:
Often fluoresces various colors, often chalky appearing (LW and SW)

Hope this helps.


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 Post subject:
PostPosted: Wed Jan 30, 2008 12:15 pm 
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Barbra Voltaire wrote:
What you have done with the refractive index is positively rule out aqua.
There are not many possibilites for a singly refractive stone with an RI of 1.50 and SG of 2.50
Actually, looking at the GLASS table in Dedeyne's Tables of Gemstone Identification it is corresponding to what one would expect for glass.

Perhaps you are misinterpreting the nature of the inclusions.
Also check for any small conchoidal fractures on the stone.
Glass is often warm to the touch. If you put a stone on your forehead it feels cool. When you put a piece of glass on your forehead it feels room temperature.

There is also the Dick Hughes hair test. Wrap a piece of hair around the stone. If it's glass the hair will burn when you try to ignite it with a match, if it is a stone it will not. That stems from a quick test to tell the difference between a jade bangle and an imitation glass bangle in Burma.


Ok, I got out my aqumarines and started touching them on my forehead as silly as that feels. I have never heard of that one before. Sure enough, the bona fide aqua's feel very cool when I put them on my forehead and this "thing" does not. It also feels a little light for it's size but that's pretty subjective.

I don't have a very expensive refractometer but in response to the other post I have rotated it in all directions on the prism and twisted the polarizer in all directions and as best as my eyes can tell it's steady at 1.50 regardless of stone orientation or polarizer orientation.

It does have an odd inclusion of some sort that I can't make out under the 30x loupe, it would take a microscope to get a good look at it and I don't have one. Maybe it could be some artifact of glass manufacture??? To be honest I have never looked at a lot of glass. As far as the bubbles go, it does have (what I call) bubbles but they look just about exactly like what you see in natural aqua under 30x.

This has an excellent cut, with very flat facets and good polish as viewed under 30x so I guess someone went to a lot of effort to cut a glass. I have just never seen glass flash with the silvery blue green brilliance typical of aqua but maybe this is just the best cut piece of glass I've ever been exposed to. Maybe I should just start cutting glass because it really looks great??? I guess maybe I am just in disbelief that something could look as good as this and just be glass.


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 Post subject:
PostPosted: Wed Jan 30, 2008 12:19 pm 
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Glass has been a convincing imitation since the time of Cleopatra.


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 Post subject:
PostPosted: Wed Jan 30, 2008 12:31 pm 
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Barbra Voltaire wrote:
Glass has been a convincing imitation since the time of Cleopatra.


Well, I'm new to this forum and many thanks to everyone who replied so quickly to help me identify this. I'm ready to close this one out as a very convincing glass fake.

I guess on some level I'm also disappointed that my own eyes couldn't just tell it was a fake because I've looked at a lot of aquamarine and I can usually suspect even a good fake a mile away from subtle visual cues. This one totally fooled me until I tested it.


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 Post subject:
PostPosted: Wed Jan 30, 2008 12:32 pm 
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Hi cutter,
It can be very convincing. I had one on my 20 stone exam for GIA and it had none of the typical characteristics you look for in glass. No swirl, no bubbles, no scratches, rounded or chipped facets, no orange peel. But it was SR and its RI did not fit appropriately for any other gem.

If you ever get to try it in a polariscope, it may exhibit ADR and show what is called "snake bands", a sort of criss cross of dark bands across the gem.


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 Post subject:
PostPosted: Wed Jan 30, 2008 12:47 pm 
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Carrie wrote:
Hi cutter,
It can be very convincing. I had one on my 20 stone exam for GIA and it had none of the typical characteristics you look for in glass. No swirl, no bubbles, no scratches, rounded or chipped facets, no orange peel. But it was SR and its RI did not fit appropriately for any other gem.

If you ever get to try it in a polariscope, it may exhibit ADR and show what is called "snake bands", a sort of criss cross of dark bands across the gem.


Thank you for your advice Carrie. I'm pretty much all self taught...hands on sort of person. I'm more of an artist than I am a gem expert and I greatly appreciate the help from knowledgeable GIA trained people like yourself.

I wanted to do the GIA courses but it was way way beyond my budget !


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 Post subject:
PostPosted: Wed Jan 30, 2008 1:04 pm 
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Hi,
have you thought to obsidian? of course as a natural glass the caracteristics will match and, personally i saw many obsidians looks like that. the only difference was a more green light blue.
just my 2c
ciao
alberto


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 Post subject:
PostPosted: Wed Jan 30, 2008 1:10 pm 
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RAVIRUS wrote:
Hi,
have you thought to obsidian? of course as a natural glass the caracteristics will match and, personally i saw many obsidians looks like that. the only difference was a more green light blue.
just my 2c
ciao
alberto


I had not considered obsidian but now that you mention it apparently both the RI and the Specific Gravity fall of this thing within the expected values for obsidian (1.5 and 2.3-2.6 respictively). As I said, in real life this stone looks more light green blue in the picture, so I guess I haven't ruled out obsidian either unless someone has a way to rule that out.


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 Post subject:
PostPosted: Wed Jan 30, 2008 1:10 pm 
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Happy to be of help cutter and glad to have you on the forum. GIA is great but there is lots you can learn on your own. Lots of free info in the links to the left of your screen and many helpful people here on the forum. I learn something new here everyday.

If you do ever want some of the GIA material just for reference, I see various course material for sale on Ebay quite often for reasonable prices. You won't get credit like you would signing up directly with GIA but you could pick up a colored stone lab manual that has some helpful info for separating gems. Also the Liddecoat book "Handbook of Gem Identification" is up for auction sometimes too. (all the standard Ebay cautions apply, pick your seller carefully, etc.)

Best-Carrie


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 Post subject:
PostPosted: Wed Jan 30, 2008 1:47 pm 
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Carrie wrote:
Happy to be of help cutter and glad to have you on the forum. GIA is great but there is lots you can learn on your own. Lots of free info in the links to the left of your screen and many helpful people here on the forum. I learn something new here everyday.

If you do ever want some of the GIA material just for reference, I see various course material for sale on Ebay quite often for reasonable prices. You won't get credit like you would signing up directly with GIA but you could pick up a colored stone lab manual that has some helpful info for separating gems. Also the Liddecoat book "Handbook of Gem Identification" is up for auction sometimes too. (all the standard Ebay cautions apply, pick your seller carefully, etc.)

Best-Carrie


all good info, thanks. The thing for me is that I work almost exclusively on Aquamarine. I know, it's weird...it's the one I like. So I know a fair amount about aqua from hands on but not so much about anything else. The most common "fake" of aqua is blue topaz but it's real easy to tell that from aqua.

Do you think this could be obsidian? Any way to rule that out?


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