[Rockhounds] 18 sided Beryl crystal

[Peter Richards]

I have no idea what a hexagonal tripyramid would be!  A hexagonal bipyramid is an approximately conical objext with a six-sided pyramid at each end.  A hexagonal tripyramid would have to have three ends(?).  There is also no single crystal form for beryl that is a prism (not pyramid) with 18 faces.  This would have to be a combination of a prism and a di-hexagonal prism, the first with 6 and the second with 12 sides.  Such a crystal is possible given the symmetry of beryl, but certainly uncommon.  However, the picture shows a beryl with a groove at the right end, probably due to its growing up against another beryl or something else.  This is not really a true face.  What I see, at least from the angle of the picture, is a simple hexagonal prism with growth imperfections.

Sorry….

Pete Richards
___________________________
R. Peter Richards, Ph.D.
rpr at heidelberg.edu
Morphological Crystallographer

> On Mar 5, 2019, at 2:46 PM, <larryrush at att.net> <larryrush at att.net> wrote:
> 
> I acquired this piece many years ago, in a trade. It may be described as a
> hexagonal tripyramid (?). Although it does have 18 prism faces, few are of
> the same width, and the symmetry is not obvious or easily defined.  The
> locality is the Mc Ginnes Mine, Wentworth, Grafton Co., NH, noted for these
> unusual beryls. It is 2X3X13 cm in size, and has no terminations.
> 
> 
> 
> I got it due to its unusual habit, and would appreciate any comments that
> help to define it, crystallographically.
> 
> 
> 
> <https://www.irista.com/gallery/sdsy1wlie6l5>
> https://www.irista.com/gallery/sdsy1wlie6l5 
> 
> Larry
> 
> 
> 
> Larry Rush
> 
> BS Geology
> 
> ConnRox Minerals
> 
> Guilford, CT
> 
> 
> 
> 
> 
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