it has alot to do with the molecular compound of the metal microwaves work at a super high microwave frequencies that makes the water molecules jump around super fast causing friction there fore makeing that object heat up well aluminum and most metals have a certain % of water molecules causeing a negitive reaction therfore causeing sparkage .. the metal the microwave in lined with is specially formulated without impurities and no water molecules
if you want to see something cool just put a egg on for a min or so //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif