My chickens free range, but the dirt here is the red, hard, clay type. I am afraid there is no place for them to get grit. I bought some that was just labeled bird grit. It looked to be the same size as the chick grit, but was turquoise. I asked at several feed stores if they carried chicken grit. They all keep giving me the same stuff. Is the "adult grit" the same size as the stuff that is labeled for chicks?