Geode

The Pulpí Geode is eight metres wide, two metres high and two metres deep. "When it comes to a geode, by definition, this is the biggest ever discovery," she noted, adding that Pulpí is not to be confused with another crystal marvel, the Naica Mine in Mexico, which has larger spars (15m long compared to Pulpí's two metres), but which is a cave lined with crystals rather than a geode. 

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 and brought it to the world's attention.

"When [the original miners] blasted this rock and found a geode, they probably got upset because they didn't like finding these crystals," said Carretero. "It meant extra work to get rid of them. They weigh a lot and were not profitable."

The story continues at the BBC.