Cave of Crystals

The Cave of Crystals is a chamber within limestone host rock inside the Naica Mine at Naica, Chihuahua, Mexico, sitting about 300 meters underground, roughly 109 meters long with a volume of 5,000 to 6,000 cubic meters. It holds giant selenite crystals of gypsum, the largest measuring 11.4 meters long with a volume of about 5 cubic meters and an estimated mass of 12 tonnes. The crystals grew from groundwater heated by a magma chamber 3 to 5 kilometers below, which saturated the water with sulfide ions; as cooler, oxygenated surface water slowly mixed in, oxygen converted the sulfides into sulfates that first precipitated as anhydrite, and once temperatures dropped below 56 degrees Celsius, the chemistry shifted to favor the growth of gypsum crystals instead, a process estimated to have taken at least 500,000 years for the largest specimens. The chamber reaches temperatures up to 58 degrees Celsius with 90 to 99 percent humidity, conditions in which unprotected visitors can endure only about ten minutes at a time. It was discovered by miners in April 2000 and reflooded with groundwater in October 2015 after mining operations ceased. This entity documents the Cave of Crystals specifically as a geological formation, a limestone chamber holding some of the largest natural crystals on Earth, grown over at least 500,000 years by hydrothermal mineral precipitation.