After sterilizing the stones by boiling, I would still proceed with caution. Limestone will slowly dissolve and raise your kH
and pH. You can test for this with a strong acid like muriatic acid. If a drop placed on the stone bubbles, then don't put it in the tank.
Another concern is metal ores, as these can be toxic to inverts and some fish. Sometimes these can be hard to identify unless you know a geologist. Most copper ores are blue or green, and some iron ores are red or orange.
Quartz, granite, sandstone, and petrified wood are all perfectly safe. HTH