How can you make chalk that can be used to write on blackboards? What are the procedures and materials?

Question

What are the procedures and materials? The chalk should be able to write well in blackboards. Please explain.

Answer 1

The mineral chalk is calcium carbonate, but blackboard chalk is actually gypsum, hydrated calcium sulphate, CaSO4.2H2O, because calcium carbonate is a little bit too crumbly. Here is what Wikipedia says:

From Wikipedia article on "Chalk": Although traditionally composed of natural chalk, modern blackboard chalk is generally made from the mineral gypsum (calcium sulfate), often supplied in sticks of compressed powder about 10 cm long.

I should imagine that small amounts of starch or some similar binder is also used, to make the particles stick together.

Answer 2

Most blackboard chalk is mined from natural deposits. It is ground to a fine powder and usually mixed with a binder to keep it from crumbling, made into a paste so it can be extruded into the common stick shape and then baked to dry and harden.