Crystal Cavern

Scientists think the giant geode began forming millions of years ago. As rainwater seeped underground, it dissolved rock, forming hollow spaces. When water breaks down rock, it’s called erosion. The water then evaporated, or changed from a liquid to a gas. The water left behind a mineral called gypsum.

Over time, more water evaporated. Gypsum particles left behind attached to each other in orderly patterns. This formed larger and larger crystals. Today, some crystals are 7 feet long! Gypsum crystals that large are very rare, explains Garcia Guinea. The only others known are found in Mexico and Chile.

The Pulpí Geode was discovered in 1999 by mineral collector Efrén Cuesta as he explored the abandoned mine. Over the years, other collectors made the journey to the geode. That eroded the geode’s entrance, making it easier to pass through.

The Pulpí Geode’s gypsum crystals are fragile. To keep them from falling apart, the air inside the geode has to stay cold and humid. Garcia Guinea is part of a group of scientists working to protect the crystals. This means limiting how many people can view the geode at a time.

Visitors are led down a spiral staircase through the mine. A pillar at the center of the stairs supports the rock. That’s important because the area is prone to earthquakes.

Unlike scientists, tourists aren’t allowed to fully enter the geode. But they can squeeze half their bodies through the opening to peek at the crystals. When Garcia Guinea first entered, he was anxious—but also excited. “My heart raced,” he says, “because I was seeing something incredible.”