What is chalk made out of?

Question

What is chalk made out of?

Answer 1

boogawooga is right & deserves "best answer"...

I just wanted to give a bit of trivia:

the CaCO3 , limestone deposit , that is used for chalk is an accumulation of microscopic spherical shells of sea organisms.

& because they are miniature ball bearings they will roll off of the piece of chalk, instead of screaching as you drag it across the chalk board

furthermore to prove that our chalk is still made of carbonate, every semester we test a variety of materials for the presence of "CO3)-2".

Baking soda, baking powder, washing soda, tums, rolaids, dolomite, limestone, abalone shell, & chalkboard chalk... all give a positive test for carbonate by generating CO2 gas upon the addition of HCl. Which is something that gypsum , CaSO4.2H2O can not do.

Answer 2

a kind of calcium carbonate (CaCO3)

Answer 3

Chalk (misnamed) used on blackboards is actually calcium sulphate dihydrate (Gypsum) however chalk deposits are generally calcium carbonate from marine organisms.