Looks like your rock didn't intersect the glass in a big enough way. 'Cos you've got that red sliver there, so you must have managed to 'cut' it out of the glass somehow! Might be my imagination, but I think I can see where the slver is missing from the glass - on the backside of it, on the right hand side. Try rotating the glass a bit, and see if it becomes clearer. If that isn't the problem, I'm stumped!