Chalks are used for writing on the blackboard. In the old days, the teachers used chalks for writing and teaching. And using a duster, the words and drawing on the blackboard could easily be erased. Therefore, using chalk was common and convenient.
Today, chalks are not commonly seen as it seems better to use the whiteboard markers. Whiteboard markers are preferred more than chalks because of cleanliness. Using chalks can be dusty, whereas, whiteboard markers do not have such problem.
When we are at Lashio, I was asked to teach an intensive course for college students. I was given chalks to use. It reminded me the old days. And at the beginning, it was challenging to use chalks. I tended to break a chalk for failing to use it tactfully.
What a challenge using the chalks to write and teach, but it is viable in a place of limited resources.