"The rock powder, usually basalt, is often scavenged from local mines or quarries, where it exists as a waste by-product. ERW companies collect the rock powder, sometimes milling it further to reduce the grain size. Then they truck it to farms, where it is used in place of ag lime.
Studies show that volcanic rock dust can raise the pH of overworked soils, improving productivity." Modern Farmer
"They're minerals Marie!"