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 Post subject: Black? Red? Cabochon
PostPosted: Tue Oct 09, 2012 10:09 pm 
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Bought 50 or so small stones at a local auction recently for study.
Cost about $50.00. Those already identified by the seller
in packets or containers proved to be as stated, according
to my tests by basic small scale equipment and most of
the others were also identified to my satisfaction by
use of equipment and GT Pro database.
Not certain as to natural or synthetic.
There are a pair of small cabochons
that are black to the eye at normal distance,
dark red up close, pinkish red with chunky,
irregular black inclusions that are
more prominent in microscopic view.
Flat bases are very black, making RI quite impossible
for me to determine. SG appears to be 2.52.
No indication of double refraction on polariscope
or dichroscope.
Many, many narrow black lines are seen clustered
together under spectroscope.
Any guesses?
Unfortunately, I am not equipped to provide pictures.


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 Post subject: Re: Black? Red? Cabochon
PostPosted: Thu Oct 11, 2012 1:06 pm 
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Location: The frozen north prairie :-/
I don't have a guess with that SG :-k . Have you considered having someone else look at them?

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 Post subject: Re: Black? Red? Cabochon
PostPosted: Thu Oct 11, 2012 2:31 pm 
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A photo isn't enough for identification, but I'm having trouble envisioning the stones from your description. Even a phone camera shot would give some idea of what they look like (and, perhaps this is just my inexperience, but generally I think photos of cabochons can potentially convey more identifying information than photos of faceted stones).

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 Post subject: Re: Black? Red? Cabochon
PostPosted: Thu Oct 11, 2012 4:24 pm 
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Thanks to you both, for today's replies. My problem appears
to have been difficulties with instruments. I have found that
both my refractometer and specific gravity device can be quite
finicky. I have now re-run the SG and found it to be closer to
2.36-2.40. This led me to obsidian on GT Pro software
and picture of mahogany obsidian which looks pretty close
to what I have. RI is given as 1.49. Rechecked on my
refractometer and got about a 1.45 which agrees with
Schumann's data. However, he shows density range of 2.35
to 2.60 which would cover the higher number I got at first.
Seems identity has been discovered.
Thanks again


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 Post subject: Re: Black? Red? Cabochon
PostPosted: Thu Oct 11, 2012 11:48 pm 
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Location: The frozen north prairie :-/
Glad the mystery is solved to your satisfaction.

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 Post subject: Re: Black? Red? Cabochon
PostPosted: Fri Oct 12, 2012 10:32 am 
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Can you post a picture of the mystery stone?


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 Post subject: Re: Black? Red? Cabochon
PostPosted: Fri Oct 12, 2012 3:58 pm 
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Sorry, Barbra - do not have setup for posting pictures.
However, if you have the GT Pro software for PC you can find
a picture under "obsidian", sub "mahogany obsidian".
Thanks for your interest.


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 Post subject: Re: Black? Red? Cabochon
PostPosted: Mon Oct 15, 2012 6:32 am 
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assuming what you have is indeed glass, and assuming that you use the spectroscope away from fluorescent light sources (led, neon tubes) and away from day light (from the window), then a glass showing many narow absorption lines is most likely artificial glass.

However I suspect you've been using your spectroscope incorrectly


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