A reasonably large and roughly terminated crystal of painite from Burma.
Up until several years ago, painite was touted as the world's rarest gemstone, with fewer than 20 carefully documented crystals having been collected since its discovery in the 1950's. Then in late 2005, there was a large find of the stuff that finally made them available to collectors.
This piece is fairly sizable, though to my mind, the roughly visible crystal shape and tapered termination make it a bit better than others.