Hey guys! OP here. Here's a follow up and a clarification. It was a single sheet of glass, about four feet long, and it fell as we were moving things around, breaking when it hit the floor. The glass shelves cost the store $200-$400 each, and we're always being reminded to be careful because they are so expensive. I was being careful, but the heavy shelf slipped in through my hands and the corner of the shelf hit the floor just right that it shattered. My boss is kind of a jerk, with a weird sense of humor. My coworker was teasing me, and my boss thought it would be funny to play along and pretend he was going to charge me for it. I posted this a little bit after it happened, before I talked to my boss, and I was pretty embarrassed, since I'm always so careful. The end of the story is that I will not have to pay for the shelf (we have tons of extras in the back, we won't miss one). Thanks for the support, everyone!