

Blackboard Chalk Isn’t Really Chalk - ForFreedom
http://gizmodo.com/blackboard-chalk-isn-t-really-chalk-at-all-1701961875?utm_source=twitterfeed&utm_medium=twitter&utm_campaign=Feed%3A+gizmodo%2Ffull+%28Gizmodo%29

======
PeterWhittaker
...it's gypsum, and while no one is really sure why gypsum replaced chalk, it
may have to do with a) gypsum being more widely available and b) gypsum can be
shaped easily by first powdering it then by adding water and shaping.

