If by shape you mean on the molecular scale, then yes. But then you say not chemical composition so lets leave the molecular scale. Above molecular scale,in lung toxicology the size and mass of inhaled particles is important. For diameters much above 2 microns the particles tend to slam into the airway walls when the path to the alveolus makes angles. They get stuck in the mucous and cilia transport it all back up to the throat where you hork it down or out. For diameters below 2 microns the particles follow the airflow gracefully to the alveoli but there they just get absorbed into the cells and disposed of like other junk. 2 microns is supposed to be a bad size, but I don't remember why, only that a toxicologist told me that long ago. And now I finally got to sound technikal. Sorry I couldn't answer your question, though. I imagine little ninja death star sharp-edged shapes could be bad.
I always suspected that "hork" was a medical term.
I can see that using chalk in an enclosed area could cause problems; but when you are outside, it doesn't seem like that big of a deal. Does it?