I was inspired by Chris Emmett's rocks to finally make one.
It still needs to be grouted, although the thinset really almost filled it in.
I used contact paper and set the tesserae into the thinset, but just could not wait for the thinset to dry, and almost immediately peeled it off. That's why the thinset looks so pitted.
Can you use just thinset and not grout? Of course, this would be outside.
I was thinking of adding some leaves too - looks a little unfinished to my eye.