May one chalk a pool cue on shabbat and yom tov? If not, why?
According to Rav Moshe Feinstein re:makeup on shabbos (where he asserts that Tochen-grinding would apply to face powders that are caked) tochen too would be a problem.
I've always heard that it's forbidden to chalk a pool cue, as it is being used for marking something. Furthermore, I've always heard that chalk is muktzah, so this is another reason against.
source: אבי מורי