Rock dust?

I was going to try my first organic grow, I have a basic growing mix already choosen. It calls for rock dust (perferabley granite or volcanic) which is the only thing that I can't seem to find at the stores I've looked around at (rural area). This maybe a really stupid question but can I use gravel dust from my lane way? (Obviously I would choose an area that doesn't get driven on, to avoid any oil contamination)

There's a lotta rock dusts around. different minerals that dissolve slowly. Best considered if you're recycling the soil. Otherwise 99.9% will still be in rock dust form.. I wouldn't use road dust

Granite dust is easy.

Landscape supply places (that sell to landscapers)

Monument shops ie: gravestones and such

Stone fabricators, like granite countertops

The landscape supply place charges me $3/5 gallon bucket for granite dust. I supply the bucket and shovel. Cows across the street so it's pretty rural.

Get looking.

Wet