Wich model software?

I am not an expert. So far I have published images-maps then following the DEM.Net tutorial I generated the 3D model then I exported it and made the useful changes. But now I’m having difficulty understanding what software to use (free) and how I can do to reproduce rocks or minerals, stones. I don’t know where to start to represent some rocks. If someone could tell me where to start, maybe I have to take numerous photographs of the chosen object (in my case the rock)? thank you very much!!