He is a Fire that has a granite pattern. Sometimes the granite pattern is due to an incomplete dominate gene (it shows up in the heterozygus form and it has a more extreme super, homozygus, form), sometimes the granite pattern is due to a dominate gene (it looks the same in the heterozygus and homozygus forms), and sometimes the granite pattern is due to the unique combination of multiple genes and is not directly inheritable (more of a line bred trait).
I would not buy a Granite female for him because you don't know if he has a granite gene, and if he does have a granite gene, you don't know if it is one of the dominate granite genes, or one of the incomplete dominate granite genes.
The wisest course of action is what Oxylepy suggested, breed him and if a female baby expresses the granite pattern, keep her and raise her up to breed back to him to see if there might be a super form. That way you know that the granite in the female is linked to the granite in the male (this course of action would not eliminate the possibility that it is a line bred trait).