Question about slate safety

[tulip55555]

Hi there. I bought a piece of slate tile from Lowes. It has a lot of metallic streaks in it, some of which looks like rust. I found this info.... Suitability of Rocks in the Aquarium - A Practical Guide ...the "heavy metals" section says that rust is safe....is this true?

 

[Fishie]

I never really heard it being "good" but I don't think it will do damage to tank maybe raise/lower PH.