Which rock type would a magnetically capable superhero move most easily?

• A. Felsic
• B. Mafic
• C. Intermediate
• D. Ultramafic

Answer: (B)

Magnetism in rocks comes from iron-rich minerals, especially ferromagnetic ones like magnetite. The more iron-bearing minerals a rock has, the stronger its magnetic response and the easier it is to move with a magnet. Felsic rocks are silica-rich and iron-poor, so they don’t respond much to magnets. Intermediate rocks have more iron than felsic but still less than mafic. Mafic rocks are richer in iron-bearing minerals, so they respond more strongly to magnetic fields and would be moved more easily. Ultramafic rocks have very high iron content and can be very magnetic as well, but among the given options mafic rocks are the clearest example of rocks that a magnet would move readily.