The World's Largest Geode Formed When the Mediterranean Sea Disappeared, New Study Reveals

By Brandon Specktor - Senior Writer 3 hours ago



A researcher stands inside the crystal-filled cave known as the Pulpí Geode — the single largest geode on Earth.
(Image: © Hector Garrido)

In an abandoned mine in southern Spain, there is a room of pure crystal.

To get there, you'll have to descend deep into tunnels, climb a ladder into an inconspicuous hole in the rocks and squeeze through a jagged tube of gypsum crystals barely wide enough for one person. If you make it that far, you'll be standing inside the world's largest geode: the Pulpí Geode, a 390-cubic-foot (11 cubic meters) cavity about the size of a cement mixer drum, studded with crystals as clear as ice and sharp as spears on every surface.

While you may have never stood inside a geode, you've probably held, or at least seen, one before.

"Many people have little geodes in their home," Juan Manuel García-Ruiz, a geologist at the Spanish National Research Council and co-author of a new paper on the history of the Pulpí Geode, told Live Science. "It's normally defined as an egg-shaped cavity inside a rock, lined with crystals."

Those crystals can form after water seeps through tiny pores in a rock's surface, ferrying even tinier minerals into the hollow interior. Depending on the size of the rock cavity, crystals can continue growing for thousands or millions of years, creating caches of amethyst, quartz and many other shiny minerals.

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