In reply to Durbs:
> I suppose ultimately "shellfish" is the answer... though depends how far you want to go back... who made the shellfish?
If the OP is trying to use
that stuff, ie: calcium carbonate - yer actual chalk, that might explain the disappointment.
The "chalk" we use for climbing isn't really chalk, it's magnesium carbonate. Incidentally, the "chalk" used for writing on a blackboard mostly isn't chalk these days either, that's gypsum.