curious question

Feller Stone has a nice variety of dried natural corals, as well as carved and rough rocks in a wide range of types and colors to choose from. A word of caution on their land-based rock materials, read the individual "Chem-Tests" reports because many are high in various elements you don't want in saltwater aquariums, such as silicon, phosphorus, iron, copper, etc.

The above was copy and pasted from:
http://saltaquarium.about.com/od/decorativecoralsrocks/index_a.htm

I'm glad I read that. I bought one for my freshwater tank a long time ago but never put it in and now I'm glad I didn't.