Every rock taken from nature or non-aquatic shop might be potentialy dangerous to your fish. You should use vinegar and spill it on the rock. If you see foam, it contains too much
calcium - this causes high water hardness level, so it is not suitable for ordinary tanks, just for African cichlids aquariums. You should put rocks into newly set-up tank with plants only. If everything goes fine for about 2-4 weeks, then the rocks are OK. You could add 1-2 fish into that tank just for testing purposes.
Anyway, my tips are different than what I did

. About 2-3 years ago I brought 10 kg of rocks from one lake in mountains and placed them into my fish tank. Naturally, no problem

. These rocks are gr8 source of algae (because algare grows on these rocks perfectly) and my small bristlenose catfish love it. .... All in all, I was lucky.
And the last note.... Rocks help water temperature to be more stable than without rocks. They have gr8 temperature persistence.