Wikipedia
Rock dust, also known as rock powders, rock minerals, rock flour, soil remineralization, and mineral fines, consists of finely crushed rock, processed by natural or mechanical means, containing minerals and trace elements widely used in organic farming practices.
The igneous rocks basalt and granite often contain the highest mineral content, whereas limestone, considered inferior in this consideration, is often deficient in the majority of essential macro-compounds, trace elements, and micronutrients.
Rock dust is not a fertilizer, for it lacks the qualifying levels of nitrogen, potassium, and phosphorus.
Rockdust is also the limestone-based product sprayed on walls inside underground coal mines to keep coal dust levels down. This is to prevent coal dust explosions and also to prevent the incidence of black lung disease.