An examination of some rare minerals from the nepheline syenites of South West Greenland

Abstract

In the present paper the mineralogy and petrological importance of some minerals from the nepheline syenites of South Greenland are discussed. The firstnamed mineral, igalikite, is from the Igaliko batholith, the remainder are from the Ilímaussaq batholith (see Ussing, 33). Igalikite was described by Bøggild from a boulder collected near Igaliko. On re-examination of this mineral it was shown to be a pseudomorph of analcime and "gieseckite" after nepheline. Naujakasite was described by Bøggild from a boulder collected at Naujakasik. The mineral has now been found in lujavrite at Tuperssuatsiaq and in the northern part of the Ilimaussaq batholith. Monazite in small clusters of angular grains are quite common in the lujavrites. The erikite described by Bøggild is shown to be a mixture of monazite and analcime and/or natrolite. Britholite has been found as small crystals in a number of altered lujavrites. Monazite and britholite are both considered to be formed at the expense of the material set free during the alteration of the eudialyte of the nepheline syenites. Neptunite in macroscopic grains is rare, but the mineral is commonly seen in thin sections, especially in rocks with altered eudialyte. The neptunite was probably formed during hydrothermal alteration of the eudialyte. A white mineral has been found at Igdlunguaq associated with neptunite, epistolite and analcime. The mineral has a primitive cubic unit cell and is probably a Na- and Nb-rich perovskite mineral. A more detailed description of this possibly new mineral will be undertaken when a chemical analysis has been carried out. Ussingite was described by Bøggild from boulders. It has now been found in place at the head of Kangerdluarssuk where it occurs in a recrystallized zone of deformation in naujaite. It is associated with steenstrupine, lovozerite (?), and ægirine and is secondary after microcline and sodalite. Lovozerite(?) a mineral resembling the lovozerite of the Kola peninsula has been found associated with the ussingite of Kangerdluarssuk and also with eudialyte in lujavrite. It is interpreted as a secondary mineral after eudialyte. Epistolite is according to a preliminary examination a member of an isomorphous series of which the murmanite of the Kola peninsula is another member.