This is a great thread. Rather than some members saying you CAN’T or SHOULDN’T make a gem or mineral specimen ID with just a photo … We have here many members working together to do just that. I congratulate everyone on this thread for making the ATTEMPT!! This is how you sharpen your observation (measurement) skills, learning, and Experience Level.
Probability is the soul of reason. These are my observations and reasoning from just the photos to form an impression of what the ID is or probably is OR what it is not.
First thing is SIZE. It is about the size of a closed fist. Some natural gems never get this big. Second, it is weathered with a matte finish (semi-transparent) [you can see the outline of his fingers through the stone] also showing rounded edges from the weathering. This stone was around water and wind for quite a long time. Third, the Color is near colorless … This can rule out stones that are always a single color in nature or that are never near-colorless in nature. There is a strong conchoidal fracture present which is also weathered. From the looks of it to my eye, this stone would be transparent if it was not weathered. There is no apparent crystal habit which indicates it is probably amorphic in internal molecular structure as well as singly refractive. From these above observations and reasoning, my impression is that this stone is a Weathered Man-Made Glass.
NOW I get out the instruments and make the confirmation to see how good my observations and reasoning was! I hope my commentary was useful to our members.