Chalk on a chalkboard is one of the worst feelings through my body but I guess it would be most limestone since chalk is made of it!
Chalk definitely creeps me out they should ban the sale and distribution of it.
Yes, especially since you rarely see the old style blackboards made of slate stone anymore.  It seems like colleges use the term blackboard for online stuff more then it is actually used.
Yeah it's not something that is used much with dry erase boards in most class rooms. Only old classrooms have it and I imagine they will be phased out.
Especially with how much technology is taking over and whiteboards being used as a writing pad and software application.