To be sure they're aquarium-safe, pour some white vinegar over them.... if they fizz, they're going to change your pH too much, so toss the fizzy ones. But, from the photo, they all appear to be ok.
What I do with rocks I find, is boil a large pot of water (no rocks). Put the rocks in the sink with the plug in... pour in enough boiling water to cover the rocks and let them sit until it's cool enough to reach in and take the plug out. You don't want to boil the rocks as there is a possibility that some could "pop" from the heat. But, the boiling water over them won't raise the internal temp high enough for that to happen, but it will take care of bacteria and nasties on the exterior of the rocks. If there's a bit of gunk on the rocks, before you pour the water over them scrub the gunk off with an old toothbrush. Don't have to be too picky, just get obvious bits.
Nice little collection you found!
Last edited by LeroyTheBetta; 05-28-2011 at 09:31 PM.