Zirconium-bearing aegirines from Motzfeldt,South Greenland

Aegirines with almost 7.0 wt.% ZrO₂ have been discovered in nepheline syenites from the Motzfeldt Centre, South Greenland. The analyses require the postulate of a new endmember pyroxene composition with the formula NaFM_0.5Zr_0.5Si₂O₆.A possible acronym is FM-NAZ. Aegirines rich in this component occur in rocks in which there is no other zirconium-bearing phase such as eudialyte.These zirconian pyroxenes have crystallised from magmas which were peralkaline, low in lime and silica and relatively low in oxygen fugacity compared with other nepheline syenites. These factors have combined to prevent the usual crystallisation of such Zr-phases as eudialyte, zircon or baddeleyite.