I ran into the need of creating realistic rocks when developing a much bigger project (https://www.artstation.com/artwork/JlEXAz).
So I decided to create a tool to generate the rocks automatically using Houdini volumes.
Now that the tool is created just need to tell Houdini of many of them I want to be cooked , wait a few seconds and pick the ones I like! :)
The output geo is highres so it is useful for both animation and videogames (as highpoly for later baking).
The color and shaders were created within Arnold.