Preparing to enter the cave is like gearing up for a space walk. I pull on a vest with more than a dozen palm-size ice packs sewn into pockets across the chest and back. Then another vest to insulate the ice against the heat. Then, over everything, a bright orange caving suit. A helmet, a headlamp, a respirator mask blowing ice-cooled air. Gloves, boots. Even for cavers cocooned in all this protective gear, the heat is exhausting and dangerous; most trips inside last no more than 20 minutes. Giovanni Badino, a physicist from the Italian exploration group La Venta, leads us in.
Fallen obelisks, pillars of light, the crystals are enormous, some several feet thick. On the floor and walls are clumps of smaller crystals, sharp as blades and flawlessly transparent. Badino proceeds slowly, careful not to damage the crystals, which are made of selenite, a form of the common mineral gypsum. Selenite is translucent and soft, easily scratched by boot heels, even fingernails. Despite the ice suits, the heat and humidity are oppressive. I remove the mask for a moment and suck in wet, hot air. My lungs want to refuse it. There is a damp, heavy scent of earth and an absolute stillness. Miserable conditions for humans, a perfect nursery for crystals.
In their architecture crystals embody law and order, stacks of molecules assembled according to rigid rules. But crystals also reflect their environment. Spanish crystallographer Juan Manuel García-Ruiz was one of the first to study the Naica crystals beginning in 2001. More familiar with microscopic crystals, García was dizzied by the proportions of the Naica giants. By examining bubbles of liquid trapped inside the crystals, García and his colleagues pieced together the story of the crystals' growth. For hundreds of thousands of years, groundwater saturated with calcium sulfate filtered through the many caves at Naica, warmed by heat from the magma below. As the magma cooled, water temperature inside the cave eventually stabilized at about 136°F. At this temperature minerals in the water began converting to selenite, molecules of which were laid down like tiny bricks to form crystals. In other caves under the mountain, the temperature fluctuated or the environment was somehow disturbed, resulting in different and smaller crystals. But inside the Cave of Crystals, conditions remained unchanged for millennia. Above ground, volcanoes exploded and ice sheets pulverized the continents. Human generations came and went. Below, enwombed in silence and near complete stasis, the crystals steadily grew. Only around 1985, when miners using massive pumps lowered the water table and unknowingly drained the cave, did the process of accretion stop.
In the presence of such beauty and strangeness, people cast around for familiar metaphors. Staring at the crystals, García decided the cavern reminded him of a cathedral; he called it the Sistine Chapel of crystals. In both cathedrals and crystals there's a sense of permanence and tranquillity that transcends the buzz of surface life. In both there is the suggestion of worlds beyond us.