The giant crystal cave

The spectacular secret treasures that have been growing beneath Mexico for 500,000 years

When miners broke through the wall of a Mexican silver mine, 300 metres underground in the year 2000, they could never have expected the site that greeted them. Enormous, translucent beams of crystal towered above them, criss-crossing from either side of a sweltering cave. Normally flooded with water, the mining company’s pumping operations had made the cave accessible to humans for the first time, uncovering the largest natural-grown crystals ever found.

The reason why the crystals had been able to grow so large is because of the precise conditions inside the cave. Lying above a magma chamber on an ancient fault line, the water inside the cave, which was rich in the mineral anhydrite, had been kept at a steady temperature of 58 degrees Celsius. At this temperature, anhydrite slowly dissolves into gypsum, a soft mineral that grows into crystals.


Geologists discovered how the crystals formed by studying tiny pockets of fluid trapped inside them


These conditions have prevailed for the past 500,000 years, allowing the gypsum crystals to grow to their impressive heights, but have also made the cave inhospitable. The high temperature and humidity means that humans can only survive inside for short periods of time, even when wearing suits lined with ice and carrying a breathing system that feeds cold air into the lungs.


Without specialist breathing equipment, moisture in the cave’s humid air would condense on the lungs


With studies of the crystals still ongoing, there is currently some debate about what to do when the Naica mine closes. Geologists must decide whether to continue pumping out the water to allow access to the cave, or let it flood again so that the crystals can continue to grow.

The cave by numbers:

Click on the image for a better look


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