Naica is a small mining town in the desert of Chihuahua, in northern Mexico. For more than a hundred years, miners worked deep under the town. They were looking for silver, lead, and zinc. Deep underground, the rock is very hot, and there is a lot of hot water inside it. So the mining company used huge pumps to pull the water out and keep the tunnels dry. In 1910, miners found a small cave with crystals about one meter long. They named it the Cave of Swords.
In April 2000, two brothers, Juan and Pedro Sánchez, were drilling in the mine about 300 meters underground. That is about as deep as the Eiffel Tower is tall. Suddenly, they came across a hidden cave. The brothers pointed their lamps inside and asked themselves what they were looking at. In the light, they saw a cave full of giant white crystals. The biggest ones were almost as long as a city bus.
The crystals are made of selenite, a clear, shiny kind of gypsum. The biggest one is about 11 meters long. For hundreds of thousands of years, the cave was full of hot water with minerals in it. Very slowly, the crystals built themselves, one tiny layer at a time. Scientists say they are some of the slowest-growing crystals ever measured. If you look closely at a photo, you can see how smooth and perfect they are.
The cave is beautiful, but it is also deadly. The air inside is about 58 °C (136 °F), and the humidity is almost 100 percent. In air like that, sweat can't cool you down, because the air is already full of water. Without protection, a person can only stay inside for about ten minutes. The heat could put their lives in danger. If you stayed too long, you could pass out.
Scientists from Mexico, Spain, Italy, and other countries came to Naica. They wanted to find out how the crystals grew so big. An Italian team designed special cooling suits for the cave. Each suit had tubes of ice-cold water and a heavy backpack full of ice, about 20 kilos. With a suit, a scientist could walk among the crystals and work for about half an hour. Then they had to get out and cool themselves off.
In 2015, mining stopped, and the company turned off the pumps. Slowly, the hot water came back and filled up the cave again. Today nobody can go inside, and the crystals are underwater once more. Some scientists think the crystals may even start to grow again. The town of Naica is still there, and people still live there today.
But the story wasn't over. In 2017, an American scientist named Penelope Boston shared a surprising discovery. Her team found tiny microbes trapped inside the crystals. In a lab, they woke the microbes up, and the microbes were still alive! They were not closely related to anything scientists knew before. Nobody knows exactly how they lived inside the crystals for so long.
Very few people have ever been inside the Cave of the Crystals. But if you search online, you can find amazing photos of the cave. You'll see scientists in cooling suits standing next to crystals that are many times bigger than they are.
If you could go inside for ten minutes, would you go?