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There is a place on Earth with such high temperature and humidity conditions that if you stay there for more than about 20 minutes, you could drown in the vapors of your own breath. I’m talking about one of our world's natural heritage sites, the Giant Cave of Crystals in Naica, Mexico.

Imagine being a miner excavating a mountain for minerals and when digging a new tunnel you come across a place that looks like superman’s cave. Can you imagine being there? Though completely immersed in water in the beginning, when the miners pumped out the water from the cave, it felt like they were walking through an alien landscape.

The Naica Cave of Crystals

The Naica Cave of Crystals is home to some enormous crystals that weigh up to about 40-50 tones and have grown to about 12 meters in length and 1 meter in width. You can get an idea about the size of these crystals when you look at the person standing next to them. The cave environment is not exactly a friendly one, but it is perfect for the growth of these giant crystals.

Giant Cave of Crystals Naica Mexico

To understand how these enormous crystals were formed, we first need to understand the geology of the region.

The Cave of Crystals is located about 290 meters underground, beneath a mineral-rich mountain close to Naica, in the state of Chihuahua, Mexico. This mountain was born about 26 million years ago when magma raised to the surface.

When that happened, the caves beneath the mountain filled with water rich in minerals. And the mineral that found the environment of this cave perfect to flourish was selenite, a form of gypsum.

What is gypsum? What is selenite?

Gypsum is a sulphate mineral with this chemical formula: CaSO4·2H2O. It is called calcium sulphate dihydrate. What this means is that for every calcium sulphate (CaSO4) molecule in the crystal structure, we find two water (H2O) molecules. As we combine more and more of these molecules, we can grow larger and larger gypsum crystals.

And when the gypsum crystal grows, we get beautiful minerals that we can often admire in the minerals sections in museums. Aren't they pretty?! I always love looking at minerals! I find it inspiring to see the beautiful structures nature creates with the help of chemistry!

gypsum minerals

The gypsum crystals can vary from colorless, clear crystals to white crystals, though sometimes there can be other hues when impurities are present in the crystal structure.

The clear crystal are the ones we refer to as selenite, and these are the crystals we find in the Giant Crystal Cave in Naica. Its chemical formula is the same as that of gypsum, but the difference between these two minerals comes from the way and the shapes under which the crystals grow.

Naica Cave Environmental Conditions

When magma raised to the surface, forming the mountain, the caves beneath the mountain filled with hot mineral-rich water. The predominant mineral was anhydrite.

Anhydrite is a calcium sulphate mineral that doesn’t contain water molecules, whereas gypsum/selenite is formed by bringing together calcium sulphate and water molecules. Anhydrite is stable above 58 degrees Celsius, while gypsum/selenite is stable below 58 degrees. In time, as the temperature started slowly decreasing below 58 degrees, anhydrite began dissolving into calcium and sulphate ions, creating a slightly supersaturated solution containing these ions.

The calcium and sulphate ions combined with the water molecules and started forming small selenite crystals. The low levers of supersaturation were ideal for the growth of few, but large, crystals. On top of that, the temperature just below 58 degrees, ideal for the transition from anhydrite to selenite, promoted the growth of selenite crystals. All in all, the cave environment ensured crystals growing larger and larger over time to form the huge selenite crystals that we see in the Giant Cave of Crystals.

Surviving in the Deadly Giant Crystal Cave

While the environmental conditions in the Cave of Crystals are perfect for the growth of giant selenite crystals, they can be very harmful to humans. Staying in that environment for more than a few minutes without some sort of protective equipment, you could actually drown in your own breath. That’s because of the difference in temperature between the temperature of the human body and the temperature inside the cave.

The average normal temperature of a human body is around 36.5 degrees Celsius (about 98 degrees Fahrenheit). So the human body temperature is much lower than that of the cave environment. That means that the air you’re breathing is hotter than the inside of your lungs. In these conditions, the humidity from the hot air will start condensing in your lungs. The fluid build-up in the lungs can lead to lung failure and that could cause death if there’s no immediate medical intervention. So if you want to go there, you’d have to wear protective cooling gear, and even with the protective equipment, you can still only stay for about 20-30 minutes.

Despite the harsh environment, it would be so cool to visit the Naica Crystal Cave, even for just a few minutes! Do you agree? Let me know in the comments below if you would also like to visit the Naica cave. However, even if we wanted to visit the giant crystal cave and had the proper authorization, we might be waiting a long time because the cave is now flooded again. The good news about the re-flooding is that the crystals are now protected again, and they are back to their preferred growth environment.

*Picture of the giant gypsum crystals of the Cave of the Crystals: Cristales cueva de Naica.JPG By author Alexander Van Driessche from Wikimedia Commons (CC by 3.0)

*gypsum crystal images - from Canva


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