Plain chalk is carcinogenic??

You have a point. Now that I went looking, most of the literature focus on silicosis, and there aren't many long-term studies that can tell us if it's carcinogenic or not.

It's very likely carcinogenic too, but now I don't know what to expect on the correlation, because it's possible that people die from it before they get the chance of developing a tumor.

I'd assume getting roughly anything in your lungs frequently enough is carcinogenic.