Mexico’s Cave of Crystal contains some of the world’s largest and most stunning natural crystal formations. Made from Gypsum, they can grow up to 36 feet long and weigh up to 50 tons. The cave, which is 950 feet underground, was sealed before discovery, which allowed the interior temperature to remain a constant 136 degrees Fahrenheit. A special door has been put in place — re-sealing the cave to prevent the crystals, which have similar properties to glass, from shattering.

The caves were discovered by a mining operation which pumped mineral-laden water out of the caverns. Let’s hope they decide to preserve this amazing natural monument.

source: National Geographic