But there’s no magic involved, just some very particular geology. The chamber contains giant selenite crystals (gypsum, CaSO4 · 2 H2O), some of the largest natural crystals ever found on Earth.

Leftover minerals from this acid bath gave rise to gypsum crystals, which formed giant blocks and delicate "flowers" in the caverns. Rain and snowmelt that seeped into the caves during the last ...