Not an expert on names of stone etc but this I think maybe a marble. Maybe Kev could help with this one.
First time I've come across graf on this surface, it's always been 95% brick. Anyway, it wouldn't remove. It's soaked in.
Tried gels, liquids, shadow chasers, wet soda blasting.
Opinions please.
EDIT: Forgot to rotate the image before hosting. But suppose it doesn't matter.