Great tips, thanks all!
I also can´t find the number of faces option...well not yet anymore, cuz yesterday I saw it somewhere
edit: ah well...it was in the rock formation properties
I figured out it is also possible to apply phototextures to the stone shaders, after fiddling with the number of repeats (sounds familiar
) you can get nice results.
I first connected a twist and shear shader and then a image map shader to the fake rock shader.
After a bit of tweaking you´ll get nice formed rocks, also with a lot of variation, and textured.