When the fluids cooled, the crystals started forming. Pulpí Geode: We take a tour inside the largest crystal 'cave' of its kind in the world.

This humongous crystal-filled cave soon became the world's largest geode, measuring 8 m (26 ft) in length! For those who don't know, Gypsum is a common mineral formed via the evaporation of seawater.

(Read about weird life found in the Cave of the Crystals.) Perhaps because of this difficulty, not everything about the Pulpí Geode’s story is crystal clear.

Pulpí, Spain, Aug 4 (EFE).- The Pulpí Geode, the largest in Europe and second in the world, has opened to visitors 20 years after being discovered in southern Spain. The crystal cave is a major ...

The geode of Pulpí was discovered in 1999 in the Mina Rica silver mine in southeast Spain. The walls of the cave are covered with huge crystals that are so transparent they look like blocks of ice.

They seem to have been made by a very specific recipe: a 250-million-year-old supply of the mineral anhydrite, a climate hospitable to crystal formation, and lots of water and time.

The geode here in Spain was originally spotted by miners in the Mina Rica, a silver mine which operated from 1873 to 1969. But it wasn't until years later, in 1999, that geologists found it again ...