how to pop the centers out of the chrome mirrors?

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so. there is a stone stuck behind my mirror face and I don't have a clue ow it got there but it did and it is stuck. and it is bugging the hell out of me. I tried a screw driver but im afraid if I pry up anymore i'm going to break the mirror How do I get the mirror face out of the mirror housing? Its the 1989-95 chrome dumbo mirrors