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Unidentified vitreous stone
  
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Joie Geurts




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PostPosted: Sep 17, 2018 12:37    Post subject: Unidentified vitreous stone  

Hello to all!

Recently while I was cleaning my mineral collection, I came across a rather peculiar stone. I’m not sure what mineral it could be, so I’d like to ask you.

I do not know when or where I got this specimen, and the lack of a matrix and a clear shape make it difficult to identify.
The stone is colourless, even though the picture suggests otherwise. The stone does, however, display a strange iridescence. The whole visible spectrum can be seen reflected in the stone as it is rotated. The blue hue suggested by the photo is one of the many colours you can see in the stone.
The mineral is vitreous, with a few opaque impurities inside. The stone has four main surfaces, though these are likely not natural. It leaves no streak.
I did some hardness tests on the stone. It does not get scratched by quartz or emerald, but did get scratched by ruby and silicon carbide. The stone does not respond to a magnetic field and does not fluoresce under shortwave UV light.

I hope that someone can help me discern what this strange stone might be. Thanks in advance for any help!



20180917_153526.jpg
 Mineral: Unknown
 Dimensions: 17*17*16 mm (furthest points)
 Description:
 Viewed:  680 Time(s)

20180917_153526.jpg


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Josele




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PostPosted: Sep 17, 2018 20:03    Post subject: Re: Unidentified vitreous stone  

Could be Labradorite.
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Joie Geurts




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PostPosted: Sep 18, 2018 05:11    Post subject: Re: Unidentified vitreous stone  

Josele wrote:
Could be Labradorite.


I don't believe this is a piece of labradorite. Labradorite is dark green and mostly opaque. This stone is clear and colourless. Labradorescence only occurs in one plane and usually displays shades of yellow, green, and blue. This stone displays reds as well and reflects light into all directions.
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Volkmar Stingl




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PostPosted: Sep 18, 2018 06:10    Post subject: Re: Unidentified vitreous stone  

This "stone" looks like glass to me.
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Joie Geurts




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PostPosted: Sep 18, 2018 06:43    Post subject: Re: Unidentified vitreous stone  

Volkmar Stingl wrote:
This "stone" looks like glass to me.


I figured this might be the case too, but glass (hardness 5.5) should easily be scratched by quartz (hardness 7) and emerald (hardness 7.5). I also tried scratching it with pyrite (hardness 6 - 6.5) just now to double-check, and the pyrite did not leave a mark. I then triple-checked by scratching actual glass with the same pyrite, and this time it did leave a mark. The stone's hardness simply does not match up with that of glass.
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Josele




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PostPosted: Sep 18, 2018 07:08    Post subject: Re: Unidentified vitreous stone  

Joie Geurts wrote:
... Labradorite is dark green and mostly opaque. This stone is clear and colourless. Labradorescence only occurs in one plane and usually displays shades of yellow, green, and blue. This stone displays reds as well and reflects light into all directions.

Can't assure nothing just from a photo of a polished piece but labradorite yes can be almost clear and can not be opaque because then it would not have labradorescence, which, in other hand, yes it can show shades of yellow, green, blue, red and any colour of the rainbow.
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Vinoterapia




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PostPosted: Sep 18, 2018 08:51    Post subject: Re: Unidentified vitreous stone  

I guess Josele is on the right track, you may want to look for the terms "sunstone" and "moonstone", both used on gemology and for some new age stuff. In any case, these terms are applied to feldspars that show transparency and colorful reflections, and yes, labradorite is included there.
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Joie Geurts




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PostPosted: Sep 18, 2018 10:15    Post subject: Re: Unidentified vitreous stone  

I did some more research on sunstones, moonstones, and feldspars in general, but the visual effects displayed by some of these minerals are not quite what I see in this stone. I can best describe the iridescence as that of a soap bubble (although I doubt this is caused by thin-film interference): colourful reflections that shift and warp as your viewing angle changes.
Also, as I've mentioned, the stone has a hardness between that of emerald (7.5) and that of ruby (9). Feldspars don't get that tough. Personally I think it might be some strange variation of topaz, which can be clear and colourless and has a hardness of 8.
I made a picture with a different (and arguably worse) camera that seems to better display the visual effect.



Foto2642.jpg
 Mineral: Unknown
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 Viewed:  477 Time(s)

Foto2642.jpg


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Vinoterapia




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PostPosted: Sep 18, 2018 10:34    Post subject: Re: Unidentified vitreous stone  

With this new picture, it actually looks man-made to me, like the titanium treated quartz.

I know you would not like it, let's hope someone else has a more concrete idea.

Good luck.
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Josele




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PostPosted: Sep 18, 2018 10:45    Post subject: Re: Unidentified vitreous stone  

After seeing this last photo, I would say it looks like an "aura quartz", that's a polished quartz pebble (natural) with a thin metallic exterior layer (artificial).
Polished stones can be very misleading...
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Joie Geurts




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PostPosted: Sep 18, 2018 13:24    Post subject: Re: Unidentified vitreous stone  

I did some searching around and I must agree with you, Josele. It does indeed seem like the stone is just metal-coated. Too bad, this makes it completely useless to me... Ah well, thanks for all the help everyone!
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lluis




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PostPosted: Sep 18, 2018 14:24    Post subject: Re: Unidentified vitreous stone  

HI, Joie

I am also wondered by piece, First pics look as transparent, last ones as coated...

I think in what Josele said..
If you could send us density, would be great... If density of a quartz, well, an "aqua Aura could be very well a good guess (as In think it is,,, I have seen here too many oddities (as broken dishes..)

With best wishes

LLuís
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Joie Geurts




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PostPosted: Sep 18, 2018 15:30    Post subject: Re: Unidentified vitreous stone  

Hi LLuís,

Sadly I don't have a precision scale or a good way of measuring volume, but I did try to approximate the stone's density using simpler methods. This gave a value of about 3.5 g/cm^3, but the accuracy of this value is questionable.
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