I'm making a species that turns the outer layers of its skin to stone, for defense purposes. It'll also have eyes that glow yellow, due to ingesting sodium vapor or helium. Is there some way to combine two processes, or do I just need to make the planet's crust or atmosphere abundant in one of the two?
Edit: would it be possible that life in mineral-rich water in caverns could lead to a build up that the creature takes advantage of? Because I've narrowed my ideas down to either that, or it forms chitin in rocky formations both as defense and as camouflage.