Cave of Crystal Giants — National Geographic Magazine:
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.
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