Cave of the Crystals of Naica, Chihuahua, Mexico

Imagine you’re a miner looking for new ore deposits deep beneath a hillside cave. You hold up your lantern, and to your surprise and astonishment, giant milky-white crystals emerge from the darkness, filling the horseshoe-shaped cave. What luck! These immense luminous crystals are larger than telephone poles. They dwarf the amazed miners and shine in all directions from the brown limestone walls, floors and ceilings of the cave. And would you know…this story really happened in Chihuahua, Mexico in 2000. 

Photography of the inside of the Cave of Crystals in Naica, Chihuahua, Mexico.
Credit: Javier Trueba/MSF/Science Source

Discovery of the Cave

The Cave of the Crystals, also known as the Giant Crystal Cave of Naica, is located 290 meters below the ground within a mountain full of lead, zinc, and silver. The cave was discovered by two brothers who worked for the Industrias Peñolas mining company. They were drilling a new tunnel and pumping out water from the mine. The Cave has become a beacon for scientists and researchers from all over the world for its unique mystery and beauty.

How the Crystals Were Formed

The Giant Crystal Cave is approximately 30 meters (98 feet) long by 10 meters (33 feet) wide–about the size of a basketball court. The cave was filled with water that was forced upward by a magma chamber deep within the Earth for tens of thousands of years. 

Illustration that shows a cross section of the Cave of Crystals.

In the magma-heated water, anhydrite deposits formed. As the water steadily cooled over time to temperatures under 136 degrees Fahrenheit, the anhydrite started to dissolve and fill the water with calcium and sulfate. When mixed with water, these molecules expand as the temperature drops, creating smooth, pure surfaces of a type of gypsum called selenite, which gives the crystals their pearl-white color.

Submerged in water, the crystals grew slowly but continuously over tens of thousands of years. This slow growth caused them to reach the massive size they are today, averaging 4 to 6 meters (13.1 to 19.6 feet) in length. But the biggest crystals in the cave are up to 11 meters (36 feet) long and 1 meter (3.2 feet) thick, about the size of the trunk of a large tree.

Illustration comparing one of the largest crystals in the Cave of Crystals with a telephone pole.

Cave of Crystals Climate

While you might want to visit the Cave to see the magnificent crystals firsthand, you’d have to put on a special suit on to keep you cool and provide breathable air. Inside the cave the air reaches 113 degrees Fahrenheit and 100% humidity, which is much too hot and moist for humans to endure for any length of time safely. The first scientists to explore the Cave could stand the environment for no longer than about ten minutes. Once equipped with cooling suits and respirators, they could extend their expeditions up to one hour at a time. 

Preservation of the Cave of Crystals

Although removing water from the Cave led to the exciting discovery of the Giant crystals and further scientific exploration, the crystals were actually much better off under water. Experiments showed that exposure to the air over two decades actually changed their structure and slowed or halted their growth. The mining company stopped pumping water out, sealed the path to the Cave, and let it refill in 2015. Two sets of doors close it off from the rest of the mine. Allowed once again to exist relatively undisturbed in their mineral-rich, watery home, we can only guess how much larger the crystals will grow. The Cave of Giant Crystals is a natural miracle worthy of preservation and recognition in our geological history.

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