In 2000, two miners working for the Peñoles mining company discovered the largest cave crystals anyone had ever seen. A fantastic assortment of sparkling gypsum formations, some more than 36 feet long and weighing up to 55 tons, were growing about a thousand feet beneath the earth at the Naica Mine in Chihuahua, Mexico. The site later came to be known as the "Cueva de Los Cristales,” or Cave of Crystals.

As Dylan Thuras of Atlas Obscura notes in the new video above, scientists estimate the crystals have been growing for half a million years. They’ve formed thanks to interactions between the magma chamber below the cave and the cool waters inside it. According to Thuras, there’s no limit to how much bigger the crystals will get.

Despite the difficulties of exploring the place—it’s more than 100 degrees inside with 100 percent humidity—scientists with the Naica Project have been conducting research on the crystals. They’ve discovered a new type of gypsum formation and looked at the DNA of ancient organisms, among other projects. However, access to the crystals might be fleeting. As Thuras notes, the crystals were revealed when the mining company pumped out groundwater to exploit the precious ores inside the cave. As soon as it doesn’t make financial sense for the mining company to leave the crystals uncovered, they will be flooded again—a return to their natural environment, but one that could leave them sadly off-limits once again.

Header image via Alexander Van Driessche via Wikipedia // CC BY 3.0