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What is the combination of hexahedronal and romb-dodecahedronal crystals called?
  
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Richard Arseneau




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PostPosted: Mar 14, 2019 17:40    Post subject: What is the combination of hexahedronal and romb-dodecahedronal crystals called?  

I am looking at the last example on this image obtained from "www smorf nl"

I was going to venture a guess, but it seems unlikely I would even be close.

Thanks for looking,

Richard

P.S. A book on crystal systems and habits is the next thing on my to-buy list.



Fluo habit.jpg
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Fluo habit.jpg


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Pete Richards
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PostPosted: Mar 14, 2019 18:45    Post subject: Re: What is the combination of hexahedronal and romb-dodecahedronal crystals called?  

There is no single name used for this combination of forms - no analog of cubeoctahedron - at least in my experience. Also, the names used for the individual forms vary, especially between parts of Europe and the USA.

We call the hexahedron the cube, and generally call the rhomb-dodecahedron just the dodecahedron.

We would name the crystal for its main form, then say "modified by the " subordinate form. Thus the top picture is of the cube modified by the dodecahedron, and the bottom one is the dodecahedron modified by the cube. We might just say "a modified cube" if we didn't know what the subordinate form was.

Note that I said THE cube and THE dodecahedron, because in the cubic symmetry system there is only one cube and only one dodecahedron (and only one octahedron). There are, however, many tetrahexahedra, many trisoctahedra, etc.

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Collecting and studying crystals with interesting habits, twinning, and epitaxy
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Richard Arseneau




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PostPosted: Mar 14, 2019 19:44    Post subject: Re: What is the combination of hexahedronal and romb-dodecahedronal crystals called?  

Thank you very much. That explains a lot, including why my searches didn't provide any results. I think I understand why you refer to the cube and the dodecahedron in the singular. In this case, we basically have two simple Platonic solids that are merged into a more complex polyhedron.

I have no idea how that form comes about, but each by itself is familiar to me. Geometry has always fascinated me, to find such beautiful examples in nature is wonderful, but hardly surprising. You have given me a great new avenue to explore.

Thanks again,

Richard
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Volkmar Stingl




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PostPosted: Mar 15, 2019 08:51    Post subject: Re: What is the combination of hexahedronal and romb-dodecahedronal crystals called?  

I would call it cubo-dodecahedron. I have some fluorite crystals from China that show this combination very well.
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PostPosted: Mar 15, 2019 18:10    Post subject: Re: What is the combination of hexahedronal and romb-dodecahedronal crystals called?  

Thanks, seems there are often differences in opinion, which is usually a healthy thing :)

The specimen I am asking about is also a fluorite from China with a very nicely formed crystal of this form.
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PostPosted: Mar 16, 2019 03:53    Post subject: Re: What is the combination of hexahedronal and romb-dodecahedronal crystals called?  

An example of that form from Northern Spain, not China


Y049 b.jpg
 Mineral: Fluorite, Calcite
 Locality:
Josefa-Veneros vein, Coroña de Arriba-La Collada, La Collada mining area, Siero, Comarca Oviedo, Asturias, Principality of Asturias, Spain
 Dimensions: 35 x 20 x 10 cm
 Description:
Crystals are up to 5cm
 Viewed:  444 Time(s)

Y049 b.jpg


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Volkmar Stingl




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PostPosted: Mar 16, 2019 06:49    Post subject: Re: What is the combination of hexahedronal and romb-dodecahedronal crystals called?  

Volkmar Stingl wrote:
I would call it cubo-dodecahedron. I have some fluorite crystals from China that show this combination very well.


Look here:
https://www.mineral-forum.com/message-board/viewtopic.php?t=754&postdays=0&postorder=asc&start=120

At this time I still called it cuboctahedral, but there are clearly cubo-dodecahedral crystals.
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