Pretty simple actually, it just took some time to get it looking right. Basically I just made a layer to lighten up everything in the top, then erased a section to make it look broken. Then I made a new layer and with a 1px white brush, I highlighted the edges of that glass and set the blending mode to Overlay. Then I did the same thing with a black brush right under the white highlight. Set it to overlay and play with the opacity until it looks right. I might have also added a glow around the edge. In that case I made a new layer and brushed a quick highlight a couple pixels wide roughly around the edge and blurred the layer then set it to overlay.