Mexican megacrystals formed by climate back-and-forth

Why are these crystals so huge? The answer is ancient climate swings.
Gypsum crystals up to 11 metres long were found a decade ago in caves next to the Naica mine near Chihuahua, Mexico. Over the past 200,000 years the regional climate has swung from wet to dry, suggests water trapped in the crystal. Ground level evaporation during the dry period concentrated calcium in salty surface water flowing into the caves. The evaporation repeated as the climate switched back and forth, providing enough calcium to build such big crystals, say Paolo Garofalo of the University of Bologna, Italy, and colleagues

Found on New Scientist