well... a couple of things offhand that it could be...
If you have a calcium rich tank, your filer feeders could be multiplying. The calcerius ones start off tiny tiny tiny, like the tip of a pin. But you'd soon notice they begin growing in a swirl pattern and develop red filters that come out of the tube.
If you are talking about white spots on your coraline, then it's the begining of blanching. This will likely grow over your rock. But there are things you can do to help save it. Since coraline is really a hard macroalgae, it needs nutrients like macro aglaes do... with one great exception... coraline needs to have phytoplankton to live... in fact, blanching is the phytoplankton being expelled from the coraline in such a degree that all the color from the photosynthetic plankton goes missing... ergo, white spots.
stocks phytoplankton in their fridges and you should ALWAYS ALWAYS have some in your own fridge. I try to remember to add some in everyday, but I usually end up adding it 2-3 times a week. You can also pick up macroaglae nutrients which will help to stimulate all your macroalgae growth and give you a healthier tank. And finally, there is coraline nutrients/stimulents and seed blocks you can buy, all will help your coraline to grow completely out of control (but don't worry, it's a good thing).
Those are the two most common "white spots on rocks" things I can think of... but if neither is right, please send more description... is it growing? are they regular shapes? are they some kind of animal growing ON the rock (do they protrude from the rock?) did your rocks come with them? is there a big fish pooping all over your rocks with white poop? are you using something that "drifts" in the tank? do you do regular gravel cleaning?
Any of those can have a hand in your white spots.