Are "Rusty" Rocks Aquarium Safe?

[Schwack]

Hi folks, hopefully this is a quick an easy question for more experienced aquarists. My house came with a bunch of leaky, broken ponds in the backyard. I've since dismantled them, but I'm left with a bunch of rock that was used to make up the various water features feeding the ponds. Some of them are visually interesting bits of rock and I was hoping to use them in a new aquarium I'm setting up for my wife. 

I've given all these pieces a good scrub in some clean water, and generally the water runs cleanly off them. If I really hit 'em with a scrub brush, they'll give off a bit of rusty tinge. They don't react to vinegar or anything like that and seem to otherwise meet the requirements for aquarium safe rock. 

Does anyone see any reason not to use this rock in an aquarium? A quick bit of research says the rust won't harm the fish, but I figured I'd throw the question to someone other than Google. Thanks all!

[Brian Scott]

Were there fish in the ponds when you moved into the house?  If not, were there fish in the ponds previously while the ponds were set up utilizing the water features these rocks came from??

[Schwack]

They kept a few goldfish, but I'm not sure these particular rocks ever got much water run over them into the ponds. They were built by an amateur (putting it kindly) and leaked like a sieve, so the water features were almost never in use.