The raw material of chalk is hydrated calcium sulfate (commonly known as gypsum).

In the production process, raw gypsum is heated to a certain temperature to partially dehydrate to form plaster of Paris, then the plaster of Paris is stirred into paste with water, and then poured into a mold for solidification. The reaction of raw gypsum to plaster of Paris is (heating):.

The reaction of gypsum plaster with water into gypsum plaster is (normal temperature):.

Extended data:

Chalk classification:

1, dust-free chalk

Dust-free chalk is an improved product of ordinary chalk, aiming at eliminating chalk dust pollution in classrooms. It just adds grease or polyol as binder to ordinary chalk, and then adds fillers with higher specific gravity, such as clay, putty, cement and so on. It can increase the specific gravity and volume of chalk dust and make it difficult to fly away, but in practical application, its effect of reducing chalk dust pollution is not very obvious.

2, non-toxic chalk

The healthiest chalk in chalk is made of pure gypsum, solidified and dried by adding water, and edible gypsum is used. At present, this kind of chalk has been used in most foreign teaching since primary school.

References:

Baidu encyclopedia-chalk