What is a critter that lives on lava?

I have a planted aquarium that consists of about 1/3 plain aquarium gravel, 1/3 lava rock, and 1/3 potting soil and succulents (rock crop, not cacti). I wanted to get a gecko but can't find info on whether or not his belly would get raw. In other words, I don't want to get some little critter that will suffer on the abbrasive lava rock, so hopefully someone could let me know a herp (or other) that would enjoy a concealed, moist, mostly humid, and well planted home. Thanks for the help!