Thanks guys
I'm glad you like it!
I have gathered some reference for sandstone boulders/rocks, so tonight I will start with those.
@Dandel0: Thanks Martin! I did not replace the voronoi and I finally also decided not to warp them because it would get too complicated and it didn't look that well either. I added a bit of billow fractal to the current ridged fractal.
You are right about the cutoff and "exploded" parts. In general you can prevent this a little by working with displacement offsets and by keeping displacement relatively mild. I've tried to be fair here, because I could also have chosen to either postwork it or to search for a POV without any of these artefacts.
One of the reasons this happens, I think, is that not every fake stone has the same base shape and size. Some stones already look a bit "sunk" from the beginning (without any texturing/displacements I mean here). I think these stones are relatively more "blown up" by the displacements I'm adding and therefore could explode or have these weird effects. Some stones look a bit facetted because of this. There's no way I can prevent this completely, but I did the best I can I think/hope
Cheers,
Martin