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About cyclic twinning - (5)
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James Catmur
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PostPosted: Sep 11, 2020 01:28    Post subject: Re: About cyclic twinning - (5)  

The Natural History Museum of Denmark, in Copenhagen, has sent me a new and better photo of their Rutile cyclic twin. I suspect it is a 'dirty dimple' and not a hole, unlike the wooden model in the same display case.

See what you think.



1893_190_Rutile.JPG
 Mineral: Rutile
 Locality:
Magnet Cove, Hot Spring County, Arkansas, USA
 Dimensions: 6cm x 3cm x 4cm
 Description:
 Viewed:  1111 Time(s)

1893_190_Rutile.JPG


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LDMarks




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PostPosted: Aug 05, 2021 11:10    Post subject: Re: About cyclic twinning - (5)  

I am looking for nice examples of fivelings, either images or references earlier than 1960 (in particular any in the 1800's). Any links very much appreciated.
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Bob Morgan




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PostPosted: Aug 05, 2021 11:42    Post subject: Re: About cyclic twinning - (5)  

Although marcasite doesn't make an exact fiveling, there are drawings in Vol. VI of Goldschmidt's Atlas der Krystallformen on Tafel 6 no's. 87, 91-95. I believe the original reports might be available on the web. They are from the 1800's.

What other minerals form fivelings?
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Pete Richards
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PostPosted: Aug 06, 2021 10:19    Post subject: Re: About cyclic twinning - (5)  

Several isometric minerals form fivelings, including diamond, copper, gold, and I think silver.
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Collecting and studying crystals with interesting habits, twinning, and epitaxy
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PostPosted: Aug 06, 2021 13:56    Post subject: Re: About cyclic twinning - (5)  

If grown by, for instance, vapor deposition then every fcc metal can produce fivelings and also icosahedra -- not as naturally formed minerals though. From Goldschmidt's atlas I found naturally occuring As, Diagond, Gold, Copper, Chalcopyrite, Marcasite and silver. Pyrite forms icosahedra only, which is odd. There seem to be many nice images of these, but few to none of fivelings.

N.B., many of the early papers are not on the web, or at least I cannot find them.
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