Difference between Cast Iron and Heavy Iron

Ah, cool. I have enough iron that I was attempting to sort it. Now that you mention that, I remember the 'heavy' being smoother. And it would be logical for cast to have a seem... It is casted. I also noticed that a strong magnet is tougher to pull off of heavy iron, and is easier to pull off of cast iron. Due to the weight difference between cast and heavy pieces of similar size, and the difference in magnetic attraction, I have come to the assumption that cast iron is an alloy. Thanks for pointing out those differences, Kz.