Aquarium safe stones???

Depends on what you mean by safe. You will want to determine if the rocks will alter water parameters--best bet is to soak the rocks in a tub of tested water, wait a week, test the water again. You can use vinegar (weak acid) to see if the rocks will alter pH, but I prefer the soaking method to be sure.

However--depending on the roadside--you'll want to clean them very, very well, and even then you might be risking adding a toxin--roadsides are frequently sprayed with pesticides and herbicides, and get all the runoff and nastiness from the road--oils, greases, rubber, etc. If this is a porous rock, I wouldn't use it, but if it's something like granite, a good cleaning should remove everything from the exterior.

i wouldnt do it if trhey were by the highway, could have tar or oils or other toxins like oriongirl was saying- pesticides and who knows what else. JMO, a good boiling and a soak in bleach dilution may work best for the cleaning. good luck!

if it bubbles with vinegar / acid it is going to change your water perams. Calciferous rocks (bubblers!) will increase yr carbonate hardness or KH

There is a lot more to this than I can competantly explain but I am sure HappyChem will notice this thread as he advised me!

Cheers
Chaz