Trivia: Blackboard Chalk Isn’t Made of Chalk



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 Blackboard chalk used to be made from natural chalk, but it has since been replaced by compressed gypsum (calcium sulfate).


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Posted on April 18, 2008 at 1:21 am by Alex
Category: Daily Trivia



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