Post subject: Re: Ruby in marble, probably from Afghanistan
Posted: Mon May 21, 2018 12:38 am
Gold Member
Joined: Sun Jun 28, 2009 9:56 am Posts: 1284
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..)
Post subject: Re: Ruby in marble, probably from Afghanistan
Posted: Mon May 21, 2018 4:21 pm
Established Member
Joined: Mon Apr 16, 2018 7:25 am Posts: 38
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.
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