I am a fan of lab testing myself but I can say for 100% certainty it is not volcanic glass. I have been machining glass for over 20 years. Glass does not fracture in perfect angles and does not form that clear on its own. The frosted coating on the outside also is a clue that its man made glass. The only real question that remains is what the prism came from. Binoculars seems to be the most probable answer given all reasonable uses for a prism that size. But good luck on the lab test.Thanks for the replies.
We will take the stone to a lab to find out more if its man made or volcanic glass.