A Mexican cave holds bus-length crystals grown over half a million years in scalding water
Miners at Naica broke into a hidden chamber in 2000 filled with selenite crystals up to 12 metres long, formed as gypsum-saturated water sat at a near-constant 58°C for roughly 500,000 years. The heat and near-100% humidity make the cave almost unsurvivable without cooling suits — explorers can last only minutes inside. The mine has since been allowed to flood again to preserve the crystals.