Chondritic ilmenite has the compositional range TiO2 51.0-54.4, FeO 35.4-44.6, MgO 1.5-6.6, MnO 0.6-9.8, Cr2O3 0.03-1.40 wt. %. Neglecting ilmenite of unusual composition (high MgO, MnO or Cr2O3), the average structural formula is (Fe1.75Mg0.23Mn0.08) (Ti1.96)O6.

Ilmenite composition shows a relation to chondrite classification: for “equilibrated” chondrites, iron content of ilmenite tends to increase as one passes from H- to L- to LL-group chondrites, whereas magnesium and manganese have the reverse tendency. Because the iron and magnesium variation is the same as observed in pyroxene, olivine and chromite of “equilibrated” chondrites, it is suggested that ilmenite is in equilibrium with these minerals. Owing to the rarity of ilmenite in ordinary chondrites insufficient data are available to detect trends within petrographic {i.e., metamorphic) subgroups; therefore, a primary igneous or a metamorphic mode of equilibration cannot be distinguished.

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