By Peter Weiss
A beautifully faceted diamond may be forever, but there are many types of facets in crystals that, until now, seemed to be never.
In most chunks of crystalline material, facets correspond to a few, highly favored planes within the lattice of atoms. Theorists have long postulated, however, that crystals with more mobile atoms or molecules could develop other, less readily formed facets, too. Those surfaces would lie at shallow angles relative to the main crystal planes.