A thousand feet (304 meter) underground, the Cave of Crystals is just one of a series of glittering caverns beneath the Chihuahuan Desert’s Naica mountain. 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. Inside the cave, it is 90 percent humidity and a temperature of 118 degrees Fahrenheit (48 degrees Celsius), which can kill an unprepared human in just 30 minutes.