The Naica Mine of the Mexican state of Chihuahua is a working mine that is known for its extraordinary selenite crystals. Located in Naica in the municipality of Saucillo, Naica is a lead, zinc and silver mine in which large voids have been found, containing crystals of selenite (gypsum) as large as 4 feet (1.2 m) in diameter and 36 feet (11 m) long.
Cave of the Crystals
The Cave of Crystals (Cueva de los Cristales) is a chamber approximately 1,000 feet (300 m) down 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 the Naica fault, which they were worried would flood the mine.
The Cave of Swords
The Cave of Swords is another chamber in the Naica Mine, also containing gypsum crystals but each only about a yard (a meter) long.
Cave of the Crystals or Giant Crystal Cave (Spanish: Cueva de los Cristales) is a cave connected to the Naica Mine 300 metres (980 ft) deep in Chihuahua, Mexico. The main chamber contains giant selenite crystals, some of the largest natural crystals ever found. The cave’s largest crystal found to date is 11 m (36 ft) in length, 4 m (13 ft) in diameter and 55 tons in weight. The cave is 27 m (89 ft) in length and 9 m (30 ft) in width. The cave is extremely hot with air temperatures reaching up to 58 °C (136 °F) with 90 to 100 percent humidity. The cave is relatively unexplored due to the extreme temperatures and high humidity. Without proper protection people can only endure approximately ten minutes of exposure at a time.
The cave was discovered in 2000 by miners excavating a new tunnel for the Industrias Peñoles mining company located in Naica, Mexico while miners were drilling through the Naica fault, which they were worried would flood the mine. The mining complex in Naica contains some of the world’s largest deposits of silver, zinc, and lead.
The Cave of Crystals is a horseshoe-shaped cavity in limestone rock. Its floor is covered in perfectly faceted crystalline blocks, and huge crystal beams jut out from both the blocks and the floor. The only reason people can get into the caves today is because the mining company’s pumping operations keep the cave clear of water. If the pumping would be stopped, the caves will again be submerged.
In 1910 miners discovered another cavern beneath Naica, the Cave of Swords. It is located over the Cave of Crystals and contains spectacular, but smaller crystals. It is speculated that transition temperatures may have fallen much more rapidly, leading to an end in the growth of the crystals.
Formation of the crystals
Naica lies on an ancient fault and there is an underground magma chamber below the cave. The magma heated the ground water and it became saturated with minerals, including large quantities of gypsum. The hollow space of the cave was filled with this mineral rich hot water and remained filled for about 500,000 years. During this time, the temperature of the water remained very stable at over 50°C. This allowed microscopic crystals to form and grow. They continued to grow to immense sizes.