Wild collecting rocks
I'd like to collect rocks, pebbles, and sand locally for the scape of my new UNS tank. I live on the front range in Colorado so I expect everything will be clean, at least in terms of man-made chemicals. Where I live most of the local rock is granite or sandstone. My understanding is that neither of these should raise the TDS of the aquarium water. However, I would like to keep some inverts, specifically snails and shrimp. What are the odds that the collected rock leaches toxic metals (e.g. copper) into the tank?