What material is chalk made of?

Ancient chalk was usually made of natural chalk, but now it has been replaced by other substances. The composition of traditional chalk is a white precipitated calcium sulfate (CaSO4), which is not easy to decompose. These particles are bigger than dust. Inhalation of trachea can cause discomfort of nose, throat and throat, which may lead to lung cancer. Light weight, dusty and difficult to clean. In view of the shortcomings of calcium sulfate chalk, environmental protection chalk often uses calcium carbonate (CaCO3) instead of traditional calcium sulfate as raw material. Calcium carbonate is a non-toxic substance with less dust, which can be metabolized normally by human body (calcium tablets or the contents of brewed food are added with calcium carbonate). Colored chalk is a mixture of the above raw materials and pigments; Some manufacturers add talc or white powder to chalk. Original website: zh. * * */wiki/%E7% B2% 89% E7% AD% 86 YouTube: * * */Watch? v=iNOjes-fX_I

Ordinary chalk → calcium sulfate environmental protection chalk → calcium carbonate.