Chalk (rock)

England's "white cliffs of Dover" are made of chalk.

Chalk is a porous sedimentary rock. Chalk is known for being a particularly soft rock. When the channel tunnel was bored, between England and France, engineers made sure to keep their tunnel boring machines within the chalk layer, that was easier to bore.

Ground chalk is manufactured into cylinders for use in writing temporary messages.

Gymnasts and rock climbers dip their hands in bags of chalk dust as doing so increasing the friction when they need a solid grip.