Sure that you don`t have quartz? That stuff treats the polarizer test differently. Fused quartz does look like a nice glass and if you don`t have a pedigree on the glass, that`s what you may actually have.
The basic comments is that the glass is pretty free of problems as far as striae and strain is concerned.
The only other thing is that the piece is a very uniquely stressed glass. You might want to have him polish up a side to do a prism and check the index of refraction on the glass if you really want to know what you have.