Trivia: Blackboard Chalk Isn't Made of Chalk
Posted by Alex in Daily Trivia on April 18, 2008 at 1:21 am
Blackboard chalk is made of gypsum, not chalk.
Chalk is a type of limestone composed of the mineral calcite. Blackboard chalk used to be made from natural chalk, but it has since been replaced by compressed gypsum (calcium sulfate).

















