Put a little SpRinG in your step!

Useless fact of today:
Someone in class asked our Sed Professor if the chalk we buy commercially (for blackboards, rock climbing, gymnastics, etc.) is still ACTUAL chalk formed from deep marine calcareous ooze. As he was not sure, I resigned myself to a little late night exploration armed with a dish of moose tracks and my dear friend Google.

This is what I found:
Sidewalk and Blackboard "chalk" is made of gypsum.
Gymnastics, Rock Climbing, and Billiards (+ a couple other things) use "chalk" made of magnesium carbonate (for another interesting use of MgCO3 click here and read FAQ #3).
Tailor's "chalk" (used by tailors to mark clothing for alteration) is Talc (magnesium silicate).

Then of course there were these handy dandy "recipes" to make your own "chalk".