What kind of rocks for aqaurium ornaments?

[a1wonder]

I was thinking about adding rocks to give my aquarium more natural look. I heard that limestone is a no go in fish tanks. Can anyone recommend what kind of rocks that will not cause harm to my fish? I've taken a gander at the aquarium ornaments in the LFS but they all appear very fake or in neon colors.

 

[tstenback]

Slate, granite, quartz are all good for the aquarium. Just make sure you test them with vinegar before using them. If you put a couple of drops of vinegar on the rock and it fizzes then it is not suitable for the aquarium as it will increase your PH. HTH