Mexico's Crystal Cave is as breathtaking as it is hazardous, with giant crystals that stand as both natural wonders and deadly traps.

Gypsum, a key component in drywall and often used in brewing pale ale and India pale ales, has been utilized by humans for millennia. But the world rediscovered its immense beauty when miners uncovered colossal crystals, essentially huge gypsum pillars, at the turn of the 21st century.

Located 984 feet (300 meters) below Sierra de Naica Mountain in Chihuahua, Mexico, these crystals have been growing for over half a million years in the scorching heat of the cave. Many of them are so vast you could walk across them, resembling something straight out of Superman's Fortress of Solitude.

Don't bother packing your bags. Visiting these crystalline marvels is essentially impossible now. That might actually be a blessing, as the Giant Crystal Cave, while magnificent, had the potential to be a deadly trap.

Perfect Conditions

Beneath the Sierra de Naica Mountain, regional fault lines have existed for millions of years. About 26 million years ago, magma began pushing through these faults toward the Earth's surface, resulting in the formation of the mountain and the creation of its enormous crystals.

The Giant Crystal Cave is a U-shaped cavern in the limestone beneath the Sierra de Naica, measuring approximately 98 feet (30 meters) long and 33 feet (10 meters) wide. For thousands of years, groundwater filled the cave, driven upward by a magma chamber deep within the Earth. This water contained the mineral anhydrite.

At temperatures exceeding 136 degrees Fahrenheit (58 degrees Celsius), anhydrite remains stable. However, at cooler temperatures, the mineral can dissolve and later reform into gypsum — a reversible transformation.

The magma beneath the Giant Crystal Cave kept the water consistently hot. However, when the water temperature dropped slightly below 136 degrees Fahrenheit (58 degrees Celsius), the anhydrite began to break down, releasing calcium and sulfate into the water. Over time, these particles combined to form a type of gypsum known as selenite.

White-tinted selenite crystals began to dominate the cave. Since the crystals remained submerged and the water temperature stayed just shy of 136 degrees Fahrenheit (58 degrees Celsius), they were able to continue growing steadily.

The growth of these crystals wasn't instantaneous. A 2011 study suggested that, given the specific conditions of the cave, it would have taken between 500,000 and 900,000 years for a selenite crystal to reach 3.2 feet (1 meter) in diameter. Over time, however, many of the crystals reached truly remarkable sizes, with lengths ranging from 13.1 to 19.6 feet (4 to 6 meters). The largest ones grew as long as 36 feet (11 meters) and measured 3.2 feet (1 meter) in thickness.

Perilous Ground

In 1794, prospectors uncovered silver on Sierra de Naica Mountain. Soon after, lead, zinc, and gold were discovered, leading to the establishment of mining operations by the mid-19th century. In 1910, the Peñoles Mining Company stumbled upon a remarkable cave just 394 feet (120 meters) below the surface. This cave, known as "The Cave of Swords," was lined with selenite crystals, though smaller in size, reaching only about 8.2 feet (2.5 meters) in length.

The selenite crystals in the Cave of Swords likely formed in a similar manner to those in the Giant Crystal Cave, but the cave cooled much faster, limiting the size of its selenite formations.

The Giant Crystal Cave itself wasn't discovered until 2000, after the Peñoles Mining Company pumped out the water. Unbeknownst to them, the cave was filled with colossal selenite columns. Miners Pedro and Juan Sanchez became the first individuals to see the crystals when they walked into the drying cave.

It quickly became apparent that Giant Crystal Cave was not a place hospitable to humans. The air temperature soared as high as 113 degrees Fahrenheit (47.1 degrees Celsius), and the humidity approached 100 percent. The air was so saturated that any visitors who stayed too long risked having fluids accumulate in their lungs, a potentially fatal condition.

The Era of Discovery

Initially, explorers could only spend 10 minutes inside the cave due to safety concerns. However, with custom cooling suits, scientific teams were able to extend their visits. The suits provided chilled, breathable air via respirators, allowing excursions lasting from 15 to 60 minutes.

In 2008 and again in 2009, NASA Astrobiology Institute director Penelope Boston ventured into the Giant Crystal Cave. There, she helped discover microbial life forms trapped within one of the crystals, suspended in an air bubble. These microorganisms could have remained dormant for as long as 50,000 years before being discovered.

The removal of water from the cave proved beneficial for scientific research, but it may have had negative consequences for the crystals. In 2017, Peñoles ceased the pumping, allowing groundwater to return. Before that, the crystals had been exposed to air for nearly two decades. Could this have weakened their structure? Experiments on samples seem to suggest it might have. However, with the water now replenished, these extraordinary crystals may begin growing once again.