chalk is a white soft material
I remember having to use that instead of dry erase markers.
chalk is a form of limestone
I had no idea, I thought limestone was totally different.
chalk is a mineral form of calcite
I don't really know what calcite is apart from the fact that it is a mineral.
Chalk
Chalk is a soft, white, porous, sedimentary carbonate rock, a form of limestone composed of the mineral calcite. Calcite is an ionic salt called calcium carbonate or CaCO. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite shells (coccoliths) shed from micro-organisms called coccolithophores. Flint (a type of chert) is very common as bands parallel to the bedding or as nodules embedded in chalk. It is probably derived from sponge spicules or other siliceous organisms as water is expelled
dihydrate form, CaSO·2HO, derived from gypsum. Chalk sticks containing calcium carbonate typically contain 40–60% of CaCO (calcite).
Advantages and disadvantages.
As compared to whiteboards, blackboards still have a variety of advantages:
- Chalk requires no special care; whiteboard markers must be capped or else they will dry out.
- Chalk is an order of magnitude cheaper than whiteboard markers for a comparable amount of writing.
- It is easier to draw lines of different weights and thicknesses with chalk than with whiteboard