Kryptonite is no longer just the stuff of fiction feared by caped superheroes.

A new mineral matching its unique chemistry - as described in the film Superman Returns - has been identified in a mine in Serbia.

According to movie and comic-book storylines, kryptonite is supposed to sap Superman's powers whenever he is exposed to its large green crystals.

The real mineral is white and harmless, says Dr Chris Stanley, a mineralogist at London's Natural History Museum.

"I'm afraid it's not green and it doesn't glow either - although it will react to ultraviolet light by fluorescing a pinkish-orange," he told BBC News.

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