Chalk

Chalk is a type of soft rock that in school settings is typically used for writing information on blackboards.

Peeves the poltergeist was known for regularly pelting chalk at unfortunate students of Hogwarts School of Witchcraft and Wizardry who were late for class.

The face of Lord Voldemort as seen on the back of Quirinus Quirrell's head was described as appearing chalk white.

In 1996, as Dolores Umbridge fled from Hogwarts, Peeves whacked her alternately with Minerva McGonagall's walking stick and a sack full of chalk.

Appearances

 * Harry Potter and the Philosopher's Stone
 * Harry Potter and the Order of the Phoenix