Found in a Serbian mine, the mineral matches the unique chemistry of Kryptonite - sodium lithium boron silicate hydroxide - as described in the movie Superman Returns. Unlike the movie, it is white - not green - and will be named Jadarite later this year.
According to Dr Chris Stanley (a mineralogist at London's Natural History Museum) "it will react to ultraviolet light by fluorescing a pinkish-orange." Doesn't sound very threatening, does it?!