The Cueva de los Cristales (Cave of Crystals) was once buried a thousand feet below Naica mountain in the Chihuahuan Desert of Mexio. It was discovered by two miners when excavating a new tunnel for the Industrias Peñoles company back in 2000.
The cave is a purely natural formation consisting of enormous beams of translucent gypsum. Some of the beams are as long as 36 feet and weigh up to 55 tons!
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Fantastic if it's true though