I'm not 100% sure but what you should get is......

Anthrax X Normal= 100%Granite Back
Granite Back X Granite Back= 12.5%Anthrax 12.5%Anthrax-Axanthic, 50%Granite Back, 12.5%Normal, 12.5%Axanthic

Maybe but I'm not to sure about this morph, more breedings need to be made to further this mutation.

Nolan