My Minecraft screen went black and I can't click the X button. There's no way I can get rid of the window. I'm using a Mac. I've even tried deleting Minecraft but it didn't work.
The answer is pretty simple, you have black screen probably because Minecraft got freezed or stopped working, all you have to do, is click three buttons; command (the one right next to space), alt, and escape, then you should get a little window which says "Force Quit Applications", you should see all programs that are running, click Minecraft, then Force Quit, confirm that, and you're done! It worked for me.