In reply to Bill Ford-Smith:
Think you're on about Cabisol. Metolius cut their chalk with this which is a really lightweight filler/drying agent. Put it in a nice looking bag charge you a shed load.
Thing about chalk balls indoors is, to get the chalk out of them you have to tap/squeeze them, to get it to go through the membrane that holds it in. Which makes nice airborn particals, the stuff they're trying to cut down on.
Loose chalk, ie powered stuff which seems to be the fashion these days, is a nightmare too, when folk fall onto bouldering crashmats, leaving a big spill...
Personally prefer a block of chalk that i can just touch in my chalk bag. Just plain simple magnesium carbonate, but it's been banned in most centres theses days, but chalk balls are worse for airborn fine dust that you can't see...
Aw well....