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scoobydoo1
Post  Post subject: Dodecahedric Shapes  |  Posted: Thu Jun 11, 2015 3:39 pm
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I was revising some materials from my earlier years in education, and was kind of stuck on the idea of naturally occurring shapes in nature - whether, how, or why modules and minerals take on the forms that they do. More so on the shape that is dodecahedric. Just how common, uncommon, or impossible is this structure in chemicals and minerals?

Can someone provide me with some guidance?

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PhDemon
Post  Post subject: Re: Dodecahedric Shapes  |  Posted: Wed May 04, 2016 12:22 pm

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I don't think it's particularly common...

In chemicals the only examples that spring to mind are dodecahedrane (C20H20) and Si20 - a silicon analogue of the fullerenes.

As for minerals the only one I know of is pyrope, an iron/magnesium/aluminium silicate related to the garnet family of minerals.

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scoobydoo1
Post  Post subject: Re: Dodecahedric Shapes  |  Posted: Wed May 04, 2016 3:06 pm
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Thank you. I'm currently travelling in the Netherlands, and won't be able to do additional research or revise the material I have back home.

I've been giving some thought into how molecules and atomic sized particles form (semi?) stable structures. Perhaps there's something in there that could explain why certain shapes; such as that of the dodecahedral shape/structure come about.


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exchemist
Post  Post subject: Re: Dodecahedric Shapes  |  Posted: Thu May 05, 2016 8:45 am

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I think it is basically to do with energy minimisation. Atoms tend form certain characteristic numbers of bonds and the lowest energy configurations allow the appropriate number of bonds to form, maximises the separation between adjacent ones (this lowers the energy, since they are negatively charged electron clouds which repel one another) and minimises the lengths of them (maximising the nucleus-bond-nucleus, i.e. +/-/+ electrostatic attraction. Forms such as tetrahedra, hexahedra, icosahedra etc can all be seen as the best approximations to a sphere that are possible with the number of atoms (i.e. vertices) available. The presence of unbonded electrons can complicate the picture (e.g. famously the water molecule is not linear, due to 2 pairs of unbonded electrons on the oxygen atom in the middle.).


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paleoichneum
Post  Post subject: Re: Dodecahedric Shapes  |  Posted: Thu May 05, 2016 10:21 pm
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Garnet and many other minerals for Dodecahedric variations all the time

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