Blackboard ‘chalk’ are produced especially for use with blackboards in white and also in various colours. White chalk sticks are made mainly from calcium carbonate derived from mineral chalk rock or limestone, while colored or pastel chalks are made from calcium sulfate in its dihydrate form, CaSO·2HO, derived from gypsum. Chalk sticks containing calcium carbonate typically contain 40–60% of CaCO (calcite). As compared to whiteboards, blackboards still have a variety of advantages: On the other hand, chalk produces dust, the amount depending on the quality of chalk used. Some people find this uncomfortable or may be allergic to it, and according
Liquid chalk Liquid chalk The term liquid chalk refers to several different kinds of chalk: Despite the term, some forms of "liquid chalk" contain no actual chalk. Liquid chalk can be a variation of normal chalk (see: magnesium carbonate) used to improve grip for sports, such as rock climbing, weight lifting, or gymnastics. Rock climbers use liquid chalk to prevent their hands from sweating. It may be used by climbers in situations where powdered chalk is restricted. It is preferred by athletes because it remains effective longer and leaves less residue on rocks and equipment. Liquid chalk for rock climbers is made