School chalk is a stick of material, typically white or colored, used for writing or drawing on blackboards or chalkboards.
Chalk used in schools generally comes in two forms:
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White Chalk: This is most commonly made from calcium carbonate (CaCO3), which is derived from mineral chalk or limestone.
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Colored Chalk: This type is usually made from calcium sulfate in its dihydrate form (CaSO4·2H2O), also known as gypsum. Pigments are added to the gypsum to create the various colors.
Therefore, while both are called "chalk," they are composed of different materials. White chalk uses calcium carbonate, a natural mineral, while colored chalk typically uses calcium sulfate (gypsum) with added pigments.
