Tiffany Stone is also known as Bertrandite, Ice Cream Opalite, and Opal Fluorite.  It is a rare stone found only in one location in Utah which is now closed to the public.  It comes in nodules which are now crushed for the beryllium to make missile nose cones.

I have handshaped and polished this oval cabochon and wire wrapped it in 14k gold filled wire.  It measures 2-9/16"Lx1-1/4"W.