I hear rocks can explode if their boiled so i wouldn't recommend that. Find out the type of rocks they are and run them under some hot hot water or put them in a bucket and pour some boiling water on them then cool them off and scrub them and leave them to dry.
Edit: Also be sure there is no rust or copper color on the rocks cause i believe that can potentially leech into your water and cause some harm.
Clean the rocks...hot water and a magic eraser is what I use.
Put them in a bucket overnight with prime added to the water.and check the water the next day.
I have done this like 6 times and have tossed out 2 rocks out of six the ones that didnt change the water have been in my tanks for over 2 years. No problems
Well I found these at the rail road tracks, so technically they belong to the rail road. They where hauled in to build up for the tracks, so there is a ton of these rocks there. I don't think they will miss a few.
I am also thinking about using a weak bleach solution to soak them in, this should kill any bad stuff living on them. I don't know what kind of rocks they are, and what they will do to the chemistry of my aquarium. So I will do what Wrench said to check.
This is a 55 gallon and I want to do stock with Angel fish, to start with. I have not decided what other species to go with yet.
Edit: I have done a little research on identifying rocks. From what I can tell the type of rocks that these are:
such as marble are tough, with straight or curved layers (foliation) of light and dark minerals. They come in various colors and often contain glittery mica.
The have that glittery mica all through them, and it is my believe that this is the type of rocks that the rail road would use to build for track laying. Because they are strong rocks that can take a lot of punishment.
I boil some water in a kettle and pour it over the rocks in a bowl.
You can do a quick vinegar test. You put a drop of vinegar on the rock and if it fizzes it'll change your water parameters. Specifically ph I believe.