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.
Blackboard
A blackboard (also known as a chalkboard) is a reusable writing surface on which text or drawings are made with sticks of calcium sulfate or calcium carbonate, known, when used for this purpose, as chalk. Blackboards were originally made of smooth, thin sheets of black or dark grey slate stone.
Design.
A blackboard can simply be a board painted with matte dark paint (usually black, occasionally dark green). Matte black plastic sign material (known as ‘closed-cell PVC foamboard’
to facilitate soldering, removing rust, and many other applications. As an example of an unusual use, a fibreglass eraser was used for preparing an archaeological fossil embedded in a very hard and massive limestone.
Types Other.
Felt chalkboard erasers or blackboard dusters are used to erase chalk markings on a chalkboard. Chalk writing leaves light-coloured particles weakly adhering to a dark surface (e.g., white on black, or yellow on green); it can be rubbed off with a soft material, such as a rag.