Not to burst your bubble or anything but chalk ain't chalk. Whether you buy it for billiards, weightlifting, rock climbing or gymnastics its pretty much all Magnesium Carbonate. And it all works the same way. Its a drying agent.
Now I wouldn't advise using sidewalk/blackboard chalk since its pretty much nothing but gypsum. And chalk used for marking football, soccer, baseball, etc... well that could be anything, titanium dioxide maybe.