So I cleaned a pretty sizable house yesterday and the guy told me that he'd had one other guy come out before me. Then he pointed out that this guy had used acid on the grout. Well obviously that was a horrific idea, and the acid got all over the stone too. He allowed me to try a couple of tiles and acid wash them to see if I could get the rest of the tile to match. It didn't work. Whatever this guy used was strong. So there is this effervescence type white discoloration along the grout lines...
Acid on raw coquina tile
Acid on raw coquina tile