[Rockhounds] The world's largest crystal cave

[Kreigh Tomaszewski]

In abandoned silver mine in Pulpí, in Spain's south-eastern Almería
Province, lies a treasure that's not made from any precious metal at all.
Instead, what's hidden here is the world's largest geode – a natural
crystal phenomenon that has stunned scientists.

As Mila Carretero, geologist and coordinator of the Pulpí Geode, explained,
a geode is a cavity inside a rock that is covered with crystals. Sitting
against a backdrop of oversized crystal spars, she broke open a tiny rock
with tiny gems inside, to show a comparison. "It's the same as the one I
have behind me, only this one is a super-sized version," she said with a
laugh as she pointed over her shoulder.

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."

Though scientists are still researching it, they believe the whole area was
once underwater. At a certain point, volcanic activity fractured
sedimentary rocks and filled them with hot fluids. When the fluids cooled,
the crystals started forming.


https://www.bbc.com/travel/article/20220721-the-worlds-largest-crystal-cave