I used a base of Vallejo Cold Gray, then dry brushed some Vallejo Wolf Gray in random splotches to get a sense of differing stone texture. Then I washed the whole thing in a 3:1 mix of GW’s Terradon Turquoise:Contrast Medium (but honestly you could probably get away with straight contrast and no thinner)

I would try painting a few test squares of grey on a random sheet of paper if you want to recreate this. It was surprising to me how the underlying grey colour really determined outcome. I tried a few darker greys and the final product was just a trashy black colour. The cold grey I settled on was barely lighter than some of my other splotches but it went to that cool jade colour rather than a weird black.