New Mineral Named After GIA’s John Koivula
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 Post subject: Unusual Crystal
PostPosted: Wed May 22, 2019 2:04 pm 
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Kind of an unusual surface on this 10 ct. orange diamond up for auction.


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 Post subject: Re: Unusual Crystal
PostPosted: Wed May 22, 2019 4:48 pm 
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A Congo cube. The surface is a colored coating. Under the coating it may be clear or not, flawed or not.

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 Post subject: Re: Unusual Crystal
PostPosted: Wed May 22, 2019 6:05 pm 
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First time I heard of a Congo Cube. Thanks Thomas.

Is the coating diamond as well?
Looks like a secondary crystallization.
Why are all the diamonds exhibiting this secondary crystallization?
If the coating is diamond, it appears that they are all randomly oriented.

Any literature on this?


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 Post subject: Re: Unusual Crystal
PostPosted: Thu May 23, 2019 8:52 pm 
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I was talking to someone who collected diamond crystals at Tucson, and he called these "sugar cubes" and said that occasionally they had a clean octahedron inside them. He actually had one there where the octahedron was exposed.


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 Post subject: Re: Unusual Crystal
PostPosted: Fri May 24, 2019 5:16 pm 
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I did a search and they seem available. Octahedron underneath? Splain that Ricky.


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 Post subject: Re: Unusual Crystal
PostPosted: Sat May 25, 2019 3:51 pm 
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Can't really explain it. He had an example: a clean octahedral diamond surrounded by what looked like "sand" made out of diamond. The shape of the exterior is a cube. He told me they were called "sugar cubes" and they certainly looked like it. He said that sometimes when you dig into them, there is a clean octahedral diamond in them, and he had one with the edge worn away, where you could see the octahedral diamond crystal inside. if you go here: http://whistleralley.com/polyhedra/cube10.gif you can see how cutting the corners off a cube leaves an octahedron. (and you can go the other way, too.)
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 Post subject: Re: Unusual Crystal
PostPosted: Sat May 25, 2019 6:33 pm 
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Here's a couple more from the same Kasai river alluvial Congo location. At about a hundred bucks a carat, would be nice if they were cuttable to any size.


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