Tom Jacobs has released a complex eroded stone substance on Gumroad.
So, I just recently started to revisit a few graphs I did a few month ago and took another pass to improve it.
This one is based upon the Martian layered sand / mud stone rocks that are scattered everywhere at the Gale Crater.
The graph itself is not very difficult, for the layering I used the quantize node and then several distortion and warp nodes. All these where mixed together, sometimes with masks, too. For this one I was aiming towards rocks that looks like rocks in terms of hardness but rather have the look of hardened dried mud.