Nepheline, a feldspathoid, is a common mineral in silica-undersaturated igneous rocks, such as plutonic nepheline syenites and volcanic phonolites.  It is colourless in plane light with relief similar to K-feldspar, sodic plagioclase and other feldspathoids, with which it commonly occurs.  For example, in A and B, nepheline coexists with the feldspathoid cancrinite, and in plane light (A) the nepheline is colourless compared to the very pale yellow cancrinite.  In C, two nepheline phenocrysts are set in a pale-brown glassy matrix.  The nephelines have abundant inclusions of brown glass, and one has a clinopyroxene inclusion and the other an inclusion of feldspar.  Nepheline has only poorly developed cleavage, which allows for confusion with quartz, but helps distinguish nepheline from the feldspars.  Maximum interference colour of nepheline is first order grey, lower than, but similar to, feldspars and quartz.  Feldspars are biaxial, however, and nepheline is uniaxial negative (and quartz is uniaxial positive).  In addition, unlike quartz, nepheline alters readily, and fine-grained micas are visible along fractures in the nepheline in B.  A and B are from cancrinite-bearing nepheline syenite from Bancroft, Ontario and C and D are from a phonolite from Mt. Kenya. Fields of view are 2.2 mm across in A and B and 11 mm across in C and D.  A and C ppl, B and D x-nicols.