Miners have discovered a substance with the exact chemical composition as Kryptonite as described in Superman Returns.
Unfortunately…

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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So disappointing!