Hi Z Friends, I made some brushes for rock sculpting. There are some great stamps take from height maps and a really cool crack brush. Please take a look! 
mdk Rock Brushes V1
Zbrush Rocks and Stone Brushes to be used for detailing and forming rock shapes.
For use with ZBrush 4R8 P2 +
14 Brushes derived from photo height maps and hand sculpting.
Brushes are numbered to use them sequentially for a super easy workflow.
You can view a quick explanation here: https://www.artstation.com/artmdk/blog/VgVK/mdk-rock-brushes-v1
Download Other Alphas/Products - https://www.artstation.com/artmdk/store
Music by: https://soundcloud.com/durianfacemask