Chalk is a rock that one can break with bare hands. It is white. A very bright tone. It can absorb water like a sponge. It is transparent when wet. I think it is also toxic, but not dangerous since it is not food. When drawing, one half of the piece of chalk, flows downwards as white dust. The chalk dust is heavier than flour but lighter than cement. Like cement, when contact is prolonged chalk can dry the skin causing it to shred. It's lines are best, on lightly textured surfaces; glass can be to smooth, unless it is matte.