I have been a gold prospector for many years now and recently discovered "crushed rock dust" for sale at my local "farmers market". So I just had to ask. Simple answer, the stuff that I throw out form my prospecting tray is what is used to make "crushed rock dust" that is full of minerals and other formulas that help your soil more than you would think. So I started to make some by crushing the little rocks like quartz, garnite, iron and so forth into super fine dust, sprinkled this on the top soil, water as regular and what a difference that made! If you havent heard, tried or seen this you should check it out. I am making more to help in the other garden outside!