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 Post subject: Ruby in marble, probably from Afghanistan
PostPosted: Sat May 12, 2018 10:15 am 
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A specimen recently bought via eBay, ruby crystals in marble:

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Backlit by the sun:
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 Post subject: Re: Ruby in marble, probably from Afghanistan
PostPosted: Sun May 20, 2018 3:54 pm 
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octahedral crystals with [111] cleavage planes sounds more like spinel.


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 Post subject: Re: Ruby in marble, probably from Afghanistan
PostPosted: Sun May 20, 2018 4:59 pm 
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Pseudooctahedral crystal form is very typical for rubies from that locale.

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 Post subject: Re: Ruby in marble, probably from Afghanistan
PostPosted: Sun May 20, 2018 7:09 pm 
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What causes that habit, Stephen? Does it occur anywhere else?


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 Post subject: Re: Ruby in marble, probably from Afghanistan
PostPosted: Sun May 20, 2018 11:15 pm 
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I am not sure what causes it. You see the same kind of formation in those winza rubies/sapphires among other locales.

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 Post subject: Re: Ruby in marble, probably from Afghanistan
PostPosted: Mon May 21, 2018 12:38 am 
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Interesting, very misleading habit. That's why I always reserve judgment when interpretating a crystal habit just from sight, which can often be deceptive unless precisely measuring the angles (I might want to get a goniometer some day..)


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 Post subject: Re: Ruby in marble, probably from Afghanistan
PostPosted: Mon May 21, 2018 7:30 am 
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Yeah, it's really unnerving the first time you see it. 'Corundum, I thought we were friends. How could you betray me like this?'

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 Post subject: Re: Ruby in marble, probably from Afghanistan
PostPosted: Mon May 21, 2018 4:21 pm 
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Thanks guys. It's funny you should say spinel as that it what it was sold as on eBay. However, the giveaway it's corundum is the fine polysynthetic twinning lines on the rhombohedral faces, and the triangular-looking terminations have the striations at 60 degree angles to each other. The rhombohedral faces are dominant which give it the sort of pseudo-octahedral look. The prismatic faces can be seen in picture 5, which have the grooved appearance.

I got it at a very good price too.


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