I have a couple of Pelligrino's trainings...very clear and concise.

The crystal and crack fuctions were applied directly to the color map. Since I'm using a negative displacement, I had to place an 'opposite' filter between the color map and the cracks. If I use just an image map on a displacement, there's noticable stretching on certain facets of the displacement, but I like adding one to the other procedural functions. It drives a subtle color variation.

In the image above, eonite topped his rock off with a sprinkle of tree to great effect...

In this experiment, I'm combining the displaced rock with a scree like material........

Mixing a displaced material has it's own dynamics worth exploring......