Ehrm... you're not that weird. I've been craving chalk and dirt all the way through this pg. Isort of get around it by going somewhere that smells like dirt (I also like rubber) and chugging down a load of water while breathing in the smell. And chewable calcium tablets (not the orange flavoured ones but the vanilla ones) have been good for the chalk craving, and might be good for the eggshell craving too.