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 Blackboard chalk used to be made from natural chalk, but it has since been replaced by compressed gypsum (calcium sulfate).

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I want the space that this is now going to take in my mind back. I would like to replace it with my anniversary, which I keep forgetting. Thank you.
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