I live in Denver CO, and I've used volcanic rocks from Iceland and Hawaii in my tank. I also paid a stone mason to break some red flagstone for me. I guess the answer to your question is "yes", as long as you run the acid test. vinegar's acid content is very low, and it might not give you good indications on the metallic content of the rock. You may have to use some real acid from industrial cleaner section of home improvement store. This proves that the rock is safe to use in the aquarium. Having said that, there are other things to consider:
1) in mountainous regions sometimes, you may find some shale rocks. They may look tough and it would give you a nice look of rock layers in the aquarium. They are not rocks! They are mud sediments. if you boil your rocks and leave them in the water, you'll see that when you rub your fingers on them, your fingers will get muddy.
2) Flag stones might be a little better. one issue that I found with them is that they are porous, and algae builds up on them very fast and they change color. It is also very difficult to clean them (even with a brush). If you don't mind mature algae growth, they this might be ok for you. you can use rock cement to stack them up make they remain stable and don't fall on your fish.
3) Volcanic rocks are very nice, and even with algae built up they still look very beautiful.
4) I think river rocks or granite are very beautiful. I don't have much experience with them but I'm sure they are much easier to work.