In Giant Crystal Cave, Naica, Mexico (Cueva de los Cristales), there are giant selenite

In Giant Crystal Cave, Naica, Mexico (Cueva de los Cristales), there are giant selenite (gypsum CaSO. 2H2O) crystals as tall as trees! But the heat and toxic atmosphere doesn't allow you to stay there very long.
.
(TITLE FROM REDDIT r/MineralPorn)