I cannot get enough of your work. It is absolutely breath taking. I had a children's book when I was little (which I poured over for hours) that had very similar artwork. Thank you for this incredibly professional job!
My technical approach with them could be simply told like this: I paint them by constantly painting over and over, stacking up various brush strokes into a pile that looks like a rough textured rock. Afterwards I can even use things like overlay to get even more variation on the surface.
The way to know which colors and values to use and how to stack up all the brush strokes comes from real life references and artist studies. I used a lot of photography for this to get a better idea of how the rock formations work in these areas.
I actually always teach people to consider shadows and light source when doing eye highlights, but I had to break it in this one myself a bit to balance her gaze, tried to also whip her hair back to make it work better but her forehead still has a too deep shadow. I can't exactly remember why it didn't work out with realistic highlight but it was a conscious choice I had to make back then as I didn't quite find a way around it.
how the hell could this not take more than 9 hours? it's incredible, hell, this is the kinda picture that i would wanna put a frame on and hang on my wall if rainbow dash & tank wasn't in it. (don't like to bring in pony in my apartment )