Chatoyancy can occur in any gemstone. Last year I saw a
beautiful cat's-eye tanzanite. It had one of the sharpest eyes I
have ever seen and it was priced way out of my range.
Yes, Gerry, I know the color you're referring to. I've got some of
that blue/gray nearly opaque too. This chunk I'm talking about now
has no gray in it and is also highly translucent and near facet
grade. Actually some of it is facet grade but with chatoyancy. I've
cut a couple of pieces and it's very attractive. Haven't approached
the best parts of the crystal yet either. Had a CC gemologist look
at a cut piece the other day and he loved it. Of course because of
the clarity of the stuff the chatoyancy is not as strong as in the
seafoam green I have. Although that's quite clean too. I'm cutting a
piece of the green that when held from one direction is nearly clear
with a few kind of lightish spots where the ends of the tubes appear
and from another viewing angle is opaque, but the color pops out.
It's an interesting effect and an experiment I'll probably follow
through with in other stones.