Hello,
  Just to throw another solution on the pile, I've just uploaded in p.t.s-f some
macros to create rounded frusta, bifrusta, and special cases of them including
pyramids, bipyramids (of which the octahedron is one), and prisms.  The shapes
should be fully solid and suitable for transparency (if the merge option is
set). I won't post the code here, if you're interested its attached here:
http://news.povray.org/web.47d05cc68ed48011ce5ce3790%40news.povray.org

A rounded octahedron with edge radius of 0.1, suitable for transparency would be
created a la:
Round_Bifrustum(4, 1, 0, 2, 0.1, yes)

Another option, hope its helpful.

-The Mildly Infamous Blue Herring

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