Crystallography and packing.

> By the way, the cubic lattice is *not* the best use of space for a
given
> volume. A tetrahedral lattice is better. (I think that the
tetrahedral
> distribution is named after the mathematician who proved that it is
optimal
> for volume filling, but I forgot the guy's name...)
>

You are right about the tetrahedral distribution, but two intersecting
tetrahedrals make the face centerd cubic structure I was thinking of.
The other structure is hexagonal close packed. Take two tertahedrals
like in the fcc case rotate one 60 degrees and overlap. The two have
equal denisty. This all assumes spheres of equal size. If you have
different size spheres, you SOL.

Bill