Solid Glass Orb

This heavy solid piece measures 2-3/4" in length and 1-1/2" in width at its widest point. It is beautiful when illuminated from behind (as in the two windowsill photos), yet opaque on a surface with no light behind it (third photo). It is not polished to a gloss, but is smooth all around except on one end where the photos show some roughness. Perhaps it was once attached to something by that end, just a guess. This was among a group of others like it, but of different colors, at a flea market. Apparently, the purchaser didn't learn anything about them from the vendor, and this one was given to me with no information. To date I have not been able to identify its origin or use. Please comment if you can help, thanks in advance.