This is a unique and cool bath "rug."
The rocks are glued to a very thin piece of grey material that resembles a loose wool. I'd give it 5 stars but by the second day a couple of rocks had popped off when one of its corners got folded under itself. Given it's heavy weight (it's a bunch of rocks), the mat can easily damage itself when you're moving it. 
It's easy to repair if you have some construction adhesive handy.