Aenigmatite in the Ilímaussaq intrusion shows a variety of textural relations to the other mafic minerals and an unusual range in chemical compositions. The saturated and oversaturated rocks contain zoned aenigmatities with Ca, Al, Fe2+-rich cores coexisting with katophorite, and near-ideal Ti-aenigmatite rims coexisting with arfvedsonite and aegirine. The aenigmatite substitutions are outlined, and the varying chemistry discussed. A no-oxide field seems to have existed in the (log fO2, T) space for the undersaturated magma, and an arfvedsonite-aenigmatite oxygen buffer equilibrium is suggested for the coexisting Fe3+-rich aenigmatite and katophorite. This buffer was later invalidated by the stabilisation of aegirine, whereby the Fe3+-aenigmatite component broke down, causing extensive recrystallisation into near-ideal Ti-aenigmatite.
- Programområde 4: Mineralske råstoffer