I spent some time studying rock sculpting and texturing.
Dark, wet rock.
Here's a few variations of the dark wet rock I created when I tweaked the materials a slight bit.
The material I created for the dark wet boulder.
ZBrush high poly model for the dark wet rock. I went through 3 or 4 different iterations of the rock until I had something I was happy with.
Vines and a boulder mesh with the different maps.