Cave of the Crystals (Naica)

The Cave of the Crystals is a chamber about 300 m underground, connected to the Naica Mine in Chihuahua, Mexico. It is about 109 m long and is filled with giant beams of selenite, a clear form of the mineral gypsum. These are some of the largest natural crystals ever found. The biggest is about 11.4 m long and weighs an estimated 12 tonnes.

The cave is also extremely hot. Air can reach 58 degrees Celsius with 90 to 99 percent humidity, and people can only survive about ten minutes without protective gear. Miners found it in April 2000. Since 2015 the mine has been flooded again, so the cave is once more underwater.

How the crystals grew

Naica sits above a magma chamber 3 to 5 km below. The magma heated groundwater that was rich in minerals. Over a very long time, as the water cooled below about 56 degrees Celsius, gypsum crystals slowly formed. They grew at an extremely slow pace for at least 500,000 years, which is why they became so huge. Scientists still study the cave to learn how such huge crystals can form.

Discovery and exploration

Miners found another cave in 1910, the Cave of Swords, at 120 m depth, with smaller crystals about one metre long. The Cave of the Crystals was found in April 2000 by brothers Juan and Pedro Sanchez while they drilled a new tunnel. The mine pumped water out for a time, which made exploring possible, but scientists studying the caves had little time because of the heat.

On the globe

Look for Chihuahua state in northern Mexico, where the Naica Mine is.