Calculations are presented, based on modal and chemical analyses of titaniferous iron ore minerals from two localities (Skaergaard and Schmoo Lake). They show that Fe: Ti ratios are constant for granular aggregates of ilmenite and titaniferous magnetite formed at any one stage in the cooling history of the containing rock body. From this and other evidence it is concluded that the aggregates are the result of exsolution from original high-temperature cubic solid solutions. For the Skaergaard rocks, the problem of separately crystallized ilmenite, distinct from the granular aggregates, is also discussed.