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Blackboard Chalk Isn't Chalk
Ubiquitous in many classrooms since the 19th century, chalk and chalkboards are familiar to most of us. White, powdery and prone to sticking to those surfaces where it is put (and just as easy to wipe away), chalk and its accompanying board are excellent instructional aids. Notably, however, most chalk today isn’t technically chalk at all, but gypsum. Chalk and [...]