Tirkine is a nepheline syenite intrusion surrounded by sand that obscures outer contacts. It consists of an outer nepheline syenite ring displaying igneous lamination with a central nepheline syenite intrusion with no apparent directional fabric. The syenite of the ring is a biotite-hastingsite-albite-nepheline syenite within which nepheline-rich and nepheline-poor facies have been distinguished (Liegeois et al., 1991). It is cut in the southwest by an intrusion of sodalite-bearing nepheline syenite. The central intrusion is a medium- to coarse-grained titanite-biotite-hastingsite-nepheline syenite that contains enclaves of a mesocratic, coarse-grained nepheline syenite rich in kaersutite and titanite, which also occurs as a separate intrusion in the southeast. In the centre of the complex is a small body of magmatic breccia consisting of porphyritic mesocratic biotite-diopside-kaersutite malignite with inclusions of a melanocratic malignite. A neck of phonolite is present near the centre of the complex and three outcrops, one 0.5 km across, of nordmarkite occur 4 km to the north.