Cave of the Crystals,Chihuahua, Mexico

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) below the surface in Naica, Chihuahua, Mexico.

The main chamber contains giant selenite crystals (gypsum, CaSO4·2 H2O), some of the largest natural crystals ever found. The cave's largest crystal found to date is 12 m (39 ft) in length, 4 m (13 ft) in diameter and 55 tons in weight. The cave is extremely hot, with air temperatures reaching up to 58 °C (136 °F) with 90 to 99 percent humidity. The cave is relatively unexplored due to these factors. Without proper protection, people can only endure approximately ten minutes of exposure at a time.

A group of scientists known as the Naica Project have been heavily involved in researching these caverns

Naica lies on an ancient fault above an underground magma chamber 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 due to the difference in their densities. The oxygen slowly diffused into the heated water and oxidized the sulfides (S2−) into sulfates (SO42−). 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. The key to this process is the slow diffusion of oxygen from the cool, low density surface water into the hot, high density ground water

The cave was discovered by the brothers Eloy and Javier Delgado. In 1910 miners discovered a cavern beneath the Naica mine workings, the Cave of Swords (Spanish: Cueva de las Espadas). It is located at a depth of 120 m, above the Cave of Crystals, and contains spectacular, smaller (1 m long) crystals. It is speculated that at this level, transition temperatures may have fallen much more rapidly, leading to an end in the growth of the crystals.The Giant Crystal cave was discovered in 2000 by miners excavating a new tunnel for the Industrias Peñoles mining company located in Naica, Mexico, while drilling through the Naica fault, which they were concerned would flood the mine.The mining complex in Naica contains substantial deposits of silver, zinc and lead.

Two other smaller caverns were also discovered in 2000, Queen’s Eye Cave and Candles Cave, and a further chamber was found in a drilling project in 2009. The new cave, named Ice Palace, is 150 m deep and is not flooded, but its crystal formations are much smaller, with small "cauliflower" formations and fine, threadlike crystals.

All of the caves discovered currently are: Cave of Crystals, Queen's Eye, Candles Cave, Ice Palace and Cave of Swords.

For more details = Cave of the Crystals