ICE RIVER COMPLEX NEPHELINE SYENITE
British Columbia’s Ice River Complex has quite a
few unusual & scarce igneous rock types (see also ferrocarbonatite
[scroll down about 2/3 of the way on that page] & sodalite-aegirine-albite
pegmatite from there). Here’s a nepheline syenite from the Ice
River Complex. This general
lithology is commonly observed in & associated with alkaline igneous
complexes and carbonatite bodies. Nepheline syenites are alkaline, intermediate
intrusive igneous rocks. They lack quartz and K-feldspar and plagioclase
feldspar. They are relatively deficient in silica (SiO2) and
rich in alkaline elements such as Na and K. The two rock-forming minerals
in the sample shown below are nepheline (greenish-gray - (Na,K)AlSiO4)
and amphibole (black). Notice there are quite a few scattered yellowish
crystals - that’s sphene (a.k.a. titanite - CaTiO(SiO4)).
Nepheline syenite from the Late Devonian/Early Mississippian-aged Ice
River Complex in southeastern British Columbia, Canada. Greenish-gray =
nepheline; black = amphibole; yellowish = titanite/sphene. Field of view:
5.2 cm across.