Toskul

The Toskul intrusion is funnel-shaped with steep outer contacts. Leucocratic, rather homogeneous, medium- and coarse-grained, and occasionally pegmatitic, aegirine-hornblende- and trachytic hornblende-biotite-nepheline syenites are the dominant rock types. The pegmatites are concentrated in the central area and include varieties of nepheline syenite and nepheline-feldspar pegmatites. In the eastern part of the massif xenoliths of gabbro, that have been changed to diorite and syenite compositions, are preserved. The nepheline syenites generally contain 63-70% microcline perthite and 20% nepheline; hastingsite, biotite and clinopyroxene total not more than 8-13%.