The Naica Mine of the Mexican state of Chihuahua, is a working mine that contains extremely large selenite crystals.  Located in Naica in the municipality of Saucillo, the Naica Mine is a lead, zinc and silver mine operated by Industrias Peñoles, Mexico's largest lead producer. Caverns discovered during mining operations contain crystals of selenite (gypsum) as large as 1.2 m (4 ft) in diameter and 15 m (50 ft) long. Peñoles announced in October 2015 that it was indefinitely suspending operations at Naica Mine.
Currently, the high temperature is 58° C (136° F) with 99% humidity, which interferes with breathing and increases the risk of asphyxiation. Because of this, researchers can only stay up to 10 min inside the cave and longer visits require the use of a specialized suit with an oxygen supply.
Cave of the Crystals
The Cave of Crystals is a cave approximately 300 m (1,000 ft) below the surface in the limestone host rock of the mine. The chamber contains giant selenite crystals, some of the largest natural crystals ever found. The selenite crystals were formed by hydrothermal fluids emanating from the magma chambers below. The cavern was discovered while the miners were drilling through a newly drained area. The caves are closed to the public, and remain closed after a worker tried to enter the cave to steal some of the selenite, only to suffocate and die in the cave's humid and inhospitable atmosphere. After enough research on the crystals has been carried out, some of the chambers will be allowed to flood again and continue the process of crystal growth.
The Cave of Swords
The Cave of Swords is another chamber in the Naica Mine, also containing gypsum crystals but each "only" about a meter long, due to the fact that these crystals are younger and had been growing for much less time by the time they were discovered.
- Let's Talk about Crystallization in the Naica Mine, at Wikijunior books for children
- García-Ruiz, Juan Manuel, et al., 2007, Formation of natural gypsum megacrystals in Naica, Mexico, Geology, 35(4): p. 327 doi:10.1130/G23393A.1
- Van Driessche, Alexander E.S. et al., (2011). "Ultraslow growth rates of giant gypsum crystals". PNAS. 108: 15721-15726.
- "Naica: largest lead producing mine in Mexico"
- "Penoles suspends operations at Naica mine in northern Mexico". Reuters. Retrieved 14 October 2015.
- National Geographic, 2008. Cavern of Crystal Giants
- National Geographic, 2007. Giant Crystal Cave's Mystery Solved
|Wikimedia Commons has media related to Naica Mine.|
- Naica mine at Peñoles
- Naica Mine at Mindat.org
- Naica Project, comprehensive website on the Crystal Caves with geology, history, photos and videos