This feels like the set up for a dumb joke but…
Cast iron will have a rough black surface and will feel heavy for its size. It is reactive and will rust if left damp or not cleaned properly. Example
Cast aluminum will be a bright silver color. Aluminum will feel light compared to stainless steel or cast iron. Aluminum is corrosion resistant and will not rust, but may react with other acidic foods. Example
Stainless steel looks shiny like aluminum, but will feel heavier for a similarly sized vessel. Stainless steel is non reactive and will not rust or interact with acidic foods. Example.
If this was a dumb joke it better be worth it.