Diamonds are a Magical Girl's best friend. They are also friends to Mons, Doomsday Devices, space rangers, magical knights, Humongous Mecha, and regular old Robots. So if you want something to look highly advanced or incredibly magically powerful, just slap a Mineral MacGuffin on it; just like a normal MacGuffin, it doesn't even have to do anything to be neat!
You see while humanity has been fine [...] [tvtropes.org]