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
What Are Little Boys Made Of? many variant forms. For example, other versions may describe boys as being made of "snaps", "frogs", "snakes", or "slugs", rather than "snips" as above. In the earliest known versions, the first ingredient for boys is either "snips" or "snigs", the latter being a Cumbrian dialect word for a small eel. The rhyme sometimes appears as part of a larger work called "What Folks Are Made Of" or "What All the World Is Made Of". Other stanzas describe what babies, young men, young women, sailors, soldiers, nurses, fathers, mothers, old men, old women, and all folks are made of. According to