I actually didn't end up purchasing them. Seller claimed it was 100% sandstone. I got someone properly identify them, turns out it was a mix of different rocks such as granite, and other components. I didn't feel comfortable putting them in my tank because of this, I didn't want minerals leeching in the tank. It's a shame cause they are gorgeous! I guess I'm stuck with pet store rocks. I heard a family pet store that sells good rocks so I will check it out