Cave of the Crystals

Cave of the Crystals or Giant Crystal Cave (Cueva de los cristales) is a cave connected to the Naica Mine at a depth of , in Naica, Chihuahua, Mexico. It takes the form of a chamber within the limestone host rock of the mine, and is about long with a volume of . The chamber contains giant selenite crystals (gypsum, CaSO4), some of the largest natural crystals ever found. The largest is , with a volume of about , and an estimated mass of 12 tonnes. When not flooded, the cave is extremely hot, with air temperatures reaching up to with 90 to 99 percent humidity. This is comparable to temperature records in Death Valley, but with much wetter air. The cave is relatively unexplored because of these factors. Without proper protection, people can only endure approximately ten minutes of exposure at a time. The cave was discovered in April 2000 by brothers Juan and Pedro Sánchez while drilling in the mine. , the mine had reflooded and the cavern filled once more with the water rich in minerals required for the crystals to grow. A group of scientists in the Naica Project have been studying these caverns. Naica lies on a fault above an underground magma chamber which is approximately below the cave. The magma heated the ground water which was saturated with sulfide ions (S2−). Cool oxygenated surface water contacted the mineral-saturated heated water, but the two did not mix because of the difference in their densities. The oxygen slowly diffused into the heated water and oxidized the sulfides (S2−) into sulfates (SO42−) that precipitated as anhydrite (CaSO4). When the overall temperature of the cave started to drop below , the hydrothermal and sedimentary anhydrite crystals dissolved, and gypsum (CaSO4) crystals formed. The hydrated sulfate gypsum crystallized at an extremely slow rate over the course of at least 500,000 years, forming the enormous crystals found today. In 1910, miners discovered a cavern beneath the Naica Mine workings, the Cave of Swords (Cueva de las espadas).