New Rock in Fish Tank?

My Dad works at a Granite and Rock place....and he brought home some decorative rock for my niece's fish tank. Its a 10gal tank with 2 goldfish in it. We have a pump and a light. Temp is usually around 74-80Degrees. Is it dangerous to put this rock in.......Rock is "dolmite", :mica", "woodrock"(white) and "black granite"? Any help would be appreciated...Thanks in advance. I dont want her goldfish to die on her.