Source: Interesting Engineering

In 1910, at the Naica Mine in Chihuahua, Mexico in the north-central part of the country, the Peñoles Mining Company was mining for silver, zinc, and lead, when miners discovered what became known as the “Cueva de Las Espadas,” or the “Cave of Swords.”

It was an 80-meter long hallway filled with selenite crystals up to two meters long. Unfortunately, once the cave was opened to tourists, it didn’t take long before many of the delicate crystals were destroyed.

Fast forward 90 years to the year 2000 when two miners, brothers Pedro, and Juan Sanchez were working in the Naica Mine, pursuing a vein of silver 984 feet (300 meters) beneath the surface when they broke through into a subterranean chamber.

It looked quite literally like Superman’s Fortress of Solitude, as depicted in the 1978 film starring Christopher Reeve. The film’s production designer, John Barry’s foreknowledge, was truly remarkable.

Welcome to the Cave of the Giant Crystals

The giant cavern, roughly 98 feet (30 meters) long by 33 feet (10 meters) wide, contained towering selenite crystals, with some 11 meters (36 ft) high, 3.2 feet (1 meter) thick, and weighing approximately 55 tons.

It took 500,000 years for these crystals to grow, and they formed because 2 to 3 miles (3 to 5 km) beneath the mine is a pool of molten magma. Over time, the caverns became flooded by groundwater which was rich in gypsum minerals.

The heat generated by the magma caused the gypsum in the water to grow into the mammoth selenite crystals we see today.

The heat from the magma makes the cave unbearably hot for humans unless they are wearing special cooling suits. Temperatures of 136 degrees F (58 degrees C) have been recorded, and the cave has a constant relative humidity of close to 100 percent.

Even wearing specially-designed cooling suits, scientists and researchers cannot spend longer than 30 – 45 minutes in the cave. The humidity causes the moisture in the air to condense within the lungs, a condition that can be fatal. Besides cooling the body, the cooling suits also deliver a supply of chilled air.

In 2006, a team led by Paolo Forti of the University of Bologna in Italy explored the cave. The University of Bergen’s scientist Stein-Erik Lauritzen dated the crystals to at least 500,000 years, and a team measured the crystals’ extremely slow growth rate.

 A completely new form of life

At the American Association for the Advancement of Science meeting in 2017, researchers including NASA Astrobiology Institute’s director Penelope Boston announced the discovery of bacteria found embedded in some of the crystals. After reanimating these organisms, scientists concluded that they are not closely related to anything in the known genetic databases.

After 17 years with no water surrounding them, the crystals had stopped growing. But then, in 2017, Peñoles stopped pumping the water out of the cave, and it refilled, allowing the crystals to continue their slow growth.