Mineral Magnetism provides essential details of the magnetic structure and magnetic properties of terrestrial rock-forming magnetic minerals. Such knowledge underpins mineral magnetic interpretations in diverse applications in the Earth, planetary, environmental, archaeological, biological, materials, and biomedical sciences. This systematic treatment points to knowledge gaps to advocate for concerted effort to fill these gaps. Here, I summarize the state of knowledge outlined in Chapters 5–14 of Mineral Magnetism. Magnetic knowledge for the ‘big five’ magnetic iron oxide minerals is reasonable, with magnetite leading the way, although gaps exist for most minerals. Five other major magnetic minerals (Al-hematite, goethite, 4C and 3C pyrrhotite, and greigite) are much less well characterized than the ‘big five’ iron oxides; much important work remains to be done for each mineral. Little systematic magnetic property information exists for further ‘minor’ magnetic minerals and other oxide spinels. This summary is provided to motivate researchers to conduct new work to fill these gaps and continue to underpin the diverse applications to which mineral magnetism contributes.