Nepheline Syenite is an anhydrous sodium potassium alumino-silicate. This material has a big advantage over feldspar: It does not contain quartz.

Because of its sodium content, high nepheline syenite glazes tend to craze (because of the high thermal expansion of Na₂O). Also, since nepheline syenite has more alumina than most feldspars, substituting it into recipes means that on one hand a lower melting temperature is achieved while on the other a more viscous melt results because of the extra alumina.

The current version of Nepheline Syenite imported by Abbots is 200# and may promote matte effects in glazes.