This is the crystal cave of giants found in the Naica Mine, Chihuahua Mexico. These are Selenite crystals (gypsum) and are the largest crystals ever discovered. They are 1000 feet down in a limestone host rock where they are mining for lead, zinc and silver. These crystals were formed by hydrothermal fluids emanating from the magma chambers below. The miners had to drill through the Naica fault, which they were worried would flood the mine, and this is what they discovered. This mine also contains the Cave of Swords, another collection of large gypsum crystal.