Chalk, as the story above mentions, isn’t “chalk,” in the classroom blackboard sense. it is a chemical compound (though it is most commonly a different compound than that mentioned above): magnesium carbonate (mgco 3). it was in the same decade that a climber brought this compound from gymnastics to climbing. Jan 01, 2015 · this item: magnesium carbonate gym chalk (case of 36 boxes) $365.90 only 8 left in stockorder soon. gibson athletic premium block gym chalk, 1lb, consists of (8) 2 oz blocks, magnesium carbonate $13.99 Apr 24, 2017 · most of the hand chalk that athletes like gymnasts, rock climbers and weightlifters use to dry their hands is magnesium carbonate. this chalk absorbs water readily and is not the same as blackboard chalk, which is calcium carbonate. While magnesium chloride, oxide and citrate may be the more visible forms of magnesium supplements on the store shelves, you can also purchase magnesium carbonate supplements to help increase your magnesium levels. this compound is used to increase the magnesium content of certain foods too.