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Help identify clear mint colored rough stones

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Hello all- My grandmother was a rockhound and left me her collection when she passed away years ago. I know what everything is she gave me except this clear mint or blue green stone that I believed was beryl until I recently took it to a local gemologist who tested it and said it wasn't beryl but also couldn't identify for me?

The test results were 6.5 +/- hardness and 1.775 on refractive index and I've been looking up everything online but found nothing real close except possibly garnet?

Any help would be appreciated.alt text

asked Mar 25, 2015 by shovelbucket (320 points)

7 Answers

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answered Mar 25, 2015 by shovelbucket (320 points)
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answered Mar 25, 2015 by shovelbucket (320 points)
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answered Mar 25, 2015 by shovelbucket (320 points)
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answered Mar 25, 2015 by shovelbucket (320 points)
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answered Mar 25, 2015 by shovelbucket (320 points)
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The deep conchoidal fracture and lack of crystalline structure are clear indicators that this is glass. (The way to test almost definitively is by doing a hardness test and seeing if the hardness is 5.5.)

answered Mar 25, 2015 by hershel (46,460 points)

Thanks Hershel.

Here are all the test result: Hardness= 6.5 (per gemologist) Refractive Index= 1.775 Specific Gravity: 2.554

No visible air bubbles at 10X magnification.

Just did the scratch test myself (gemologist did yesterday) and while the glass does leave slight marks on the stone, the point of the glass breaks into little pieces when scratching the stone. When scratching the glass with the stone it cuts into to the glass enough to catch your fingernail tip and the stone does not break apart at scratch point or leave any of it's own particles on the glass.

Thanks again for your help!

i saw the photo and pretty much came to the same conclusion.
Hi, I didn't see anyone call it "volcanic glass" i.e. green obsidian in the rough (unpolished). The cheap glass nuggets in fish tanks is just man-made glass. Very likely your rock-hound gran would have the obsidian.
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Its glass. No crystalline structure and massive conchoidal fracture. Specific gravity is within the acceptabily of glass, and though the hardness is higher its likely the test wasn't 100% accurate or its a harder composite of glass. I don't know of any mineral with that transparency that lacks a crystalline structure. In pet shops you can buy very similar glass to this for fishtanks.

answered Mar 26, 2015 by hershel (46,460 points)

Thanks again!

 


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