Peridot can be seen licking a stone to derive information from it in this episode, at the Kindergarten. Licking rocks is actually a way to identify certain minerals and materials in those rocks; it can be used to identify Halite (which is salty) from Sylvite (which is more bitter), and it can be used to make the grains more apparent in a stone, to help determine if it is a sample of grainy sandstone or smooth siltstone or mudstone. This is unwise in most cases for humans due to bacteria and fungi in the rock and in the dirt, but for a sentient space rock like Peridot human bacteria poses no real threat.