giant crystal caves unearthed

It looks like Superman's Fortress of Solitude and is nearly as hard to get into, but that hasn't stopped explorers from uncovering new secrets in and around Mexico's deep, deadly hot Cave of Crystals.

Outfitted with ice-cooled suits, teams have found biological mysteries, parallels with other planets, and the "Ice Palace," an unexplored cavern lined with rare crystal formations—and just in time too. Parts of the complex may soon be returned to their natural, submerged states.

A thousand feet (304 meter) underground, the Cave of Crystals (pictures) is just one of a series of glittering caverns beneath the Chihuahuan Desert's Naica mountain (map). Much of the complex would naturally be filled with scorching water, were it not for industrial pumps that facilitate the mining of silver, zinc, lead, and other minerals in the caves.

In the two-story-tall, football-field-size Cave of Crystals, enormous beams of gypsum—among the largest freestanding crystals in the world—sprout haphazardly from the ceiling, floor, and walls. Individually, though, the crystals appear anything but haphazard, sporting the sharp, geometric appearance that scientists call euhedral.

This jewel-like effect makes the giant crystals truly unique, according to John Rakovan, a mineralogist at Miami University in Ohio, who was not involved in the project.

"When crystals get larger and larger, they become less euhedral, typically"—and more rocklike. "Scientists didn't think it was possible to get large crystals that are so morphologically perfect" before the Cave of Crystals discovery, Rakovan said.

The translucent columns also resemble giant pillars of ice but are warmed by superheated air leaking up from underground magma chambers.

The combination of 90 percent humidity and a temperature of 118 degrees Fahrenheit (48 degrees Celsius) inside the cave can kill an unprepared human in just 30 minutes.