Here is my new custom rock brush and alpha set for Zbrush, 18 brushes and height/alpha maps + 3 ztool rock meshes and a mini tutorial that you can read over at artstation
These brushes can be used for any program that works with alphas and height maps, add to 3Dcoat, mudbox, substance painter etc.
bigger preview pictures and mini tutorial over at - https://www.artstation.com/artist/jronn
feedback, questions, and updates at - www.facebook.com/JonasDigitalArt
(free to use for commercial use)