Watching grass grow is heart-pounding excitement compared to monitoring gypsum crystals. A team of researchers from Spain and Japan have discovered that these giants in Chihuahua, Mexico, had the slowest growth rate ever recorded for crystal: In a century, they grew just 0.04 millimeter—about the width of a human hair. Some are 36 feet long but may have taken, oh, you know, about a million years to get there. Before it was pumped out for mining in 1975, the cavern was filled with consistently hot calcium-sulfate-rich water—perfect for these crystals, which form only in a 129- to 136-degree-Fahrenheit window. But now that the cave is dry, the crystals have stopped growing. Despite its icy appearance today, the grotto hovers around 113 degrees, too hot for anyone to stand around measuring for long.