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 Post subject: Moissanite with no doubling?
PostPosted: Mon Dec 21, 2015 2:05 pm 
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So I just got a moissanite, it's indian in origin, and it tests positive on the tester, but there is zero facet doubling, at least none that I can detect with a good loupe. I was under the impression there would always be some doubling, even if it was well cut. Can a moissanite be cut well enough that it shows no doubling? Or is it possible that another material will test positive on a diamond tester (other than diamond and moissanite).


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 Post subject: Re: Moissanite with no doubling?
PostPosted: Mon Dec 21, 2015 2:11 pm 
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Nevermind, I was looking through the stone at the wrong angle. Oopsie :D


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 Post subject: Re: Moissanite with no doubling?
PostPosted: Mon Dec 21, 2015 3:09 pm 
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A little extra info, courtesy of Moissanite Co.
Image


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 Post subject: Re: Moissanite with no doubling?
PostPosted: Mon Dec 21, 2015 3:56 pm 
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Yeah, that's similar to what I found that reminded me of the angle. Thanks Barbra


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 Post subject: Re: Moissanite with no doubling?
PostPosted: Mon Dec 21, 2015 5:47 pm 
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-no doubling along optical axis
-the longer the light path, the more visible the doubling


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 Post subject: Re: Moissanite with no doubling?
PostPosted: Fri Jan 22, 2016 2:18 am 
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I've gotten a bunch of indian moissanite in recent months. Most of it is blue/green and cut such that they display strong doubling, but others are cut such that they don't. I have to admit, my favorite ones are the ones that display the doubling :) I just like weirdo stones ;)

Here's one I cut that *does* show it strongly, and another that doesn't.

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 Post subject: Re: Moissanite with no doubling?
PostPosted: Mon Apr 11, 2016 1:20 pm 
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I was told by someone in the synthetic industry that cubic system Moissanites exist, and because they are cubic like diamond, there's no double refraction. Cubic silicon carbide is one of the possible crystal polytypes and requires CVD technique to grow.


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 Post subject: Re: Moissanite with no doubling?
PostPosted: Sun Sep 10, 2017 12:11 pm 
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This is an older thread, but I thought I'd chime in. I asked one of the lab gemologist at GIA about cubic moissonite (I read about the possibility many years ago). He told me it can be made but would look Very different and would not pass as a diamond stimulant .


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 Post subject: Re: Moissanite with no doubling?
PostPosted: Sun Sep 10, 2017 9:35 pm 
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It also would go under a different mineral name.

Hexagonal carbon is never called diamond...

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 Post subject: Re: Moissanite with no doubling?
PostPosted: Sun Sep 10, 2017 11:25 pm 
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I believe the name moissanite actually refers to all the 250-ish polymorphs (similar to 'ice' referring to all the ice polymorphs).

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 Post subject: Re: Moissanite with no doubling?
PostPosted: Mon Sep 11, 2017 1:31 am 
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Isn't the historic definition of a mineral "a naturally occurring chemical compound with a fixed composition (including solid solution series) and physical properties (including crystal structure)"? Surprised the High Lords of Mineral Terminology would allow this to exist - they are SUCH sticklers for detail... But being a manufactured, commercial item it probably never came past them.

On a bit further study, seems this is an area of difference between chemistry (esp. organic)/materials science and mineralogy... Chemistry just gives different structural designations to different crystal forms of a compound (our polymorphs), Mineralogy (and normally gemology) gives them different names, like andalusite, kyanite, and sillmanite (all polymorphs of Al2SiO5)...

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 Post subject: Re: Moissanite with no doubling?
PostPosted: Tue Sep 12, 2017 1:29 pm 
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Speaking of polymorphs... I saw a boule of what I think was 6C, that was bluish purple, and another one that was yellowish-green (maybe 4H?). Totally different colours but both looked like the standard hockey pucks.


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 Post subject: Re: Moissanite with no doubling?
PostPosted: Sun Sep 17, 2017 10:14 am 
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Lonsdaleite: hexagonal diamond


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