Apparently this has already been kind of tested (underground too!)

I took a tour of the Wieliczka salt mine when I was in Poland 10 or 15 years ago. As we started to enter the actual mine, the tour guide said something like :

The roof is salt, the floor is salt, the walls are salt, everything is salt. Lick the wall if you want, it's salt."

pauses for a few seconds while somebody licks the wall

Now I should inform you that I tell that to every single group I take through here and every single time at least one person licks the walls.