If you tap the very corner of the screen against one of your front teeth, you can tell it's glass. Very hard sharp sound. Plastic always feels different, even very hard plastic.
Try it yourself, very gently of course and right on the outside corner of the screen.
What I have noticed, and it's only under really bright light, is that you can see lots of little lines on the screen. I thought they were scratches at first, but they cover the entire screen. They run in parralel dashed lines.





