Chalk: the white stick used to write on blackboards. It can also refer to the powder (magnesium carbonate) climbers use to reduce slipping.
先生は黒板にチョークで例文を書いた。
The teacher wrote example sentences on the blackboard with chalk.
ボルダリングの前に手にチョークをつける。
Before bouldering, I put chalk on my hands.
チョークの粉が服に付いてしまった。
Chalk dust got on my clothes.