I take rocks from different places all the time and pop them in my tanks. Doesnt seem to matter what type they are so long as they are boiled. We boil them for 20 - 30 min and then rinse them with tap water before putting them into the tank. We've had no problems with fish deaths, algae or rust. If you didn't boil them you may have introduced some microbes that could have killed your fish, especially if the rocks came from outdoors near water.
If the rocks were kept indoors they may have been treated with something rinsing wont take off entirely. You could also be using a bad type of stone that seeps into the water like limestone or something in which case the rock itself may be giving off deadly vibes.