IN NAICA, MEXICO, THERE ARE SELENITE CRYSTALS AS LARGE as twelve meters long, weighing as much as fifty-five tons. Naica rests atop an underground magma chamber, and intense amounts of heat and pressure have formed the crystals there over the past 500,000 years. Until the year 2000, the cave was flooded with water and unexplored. Silver, zinc, and lead miners in Naica found and drained the cave and its nearby sisters, which include the Cave of Swords, containing smaller, sharper crystals, and the Ice Palace, which is filled with even smaller, threadlike crystals.
Selenite, a variety of the mineral gypsum, is very soft, so soft that it can be scratched with a fingernail. These giant selenite crystals are used to being in water, and they are now deteriorating in the hot, dry air, so scientists are studying the cave as quickly as possible. The cave will likely be filled with water again as soon as the nearby silver and lead mines are exhausted. In order to bear the heat—which can rise to a debilitating 136 degrees in the caves—scientists must wear refrigerated suits, but the cooling period only lasts for half an hour at a time, so it’s difficult to get any real work done. For quite some time, researchers were unable to find any sort of organic matter in the cave, but in 2017 scientists were able to extract and reanimate bacteria embedded in some of the crystals; the bacteria are not closely related, genetically, to any other known species.