Nepheline Syenite (K2O×3Na2O×4AlO3×9SiO2) is a common flux chemically similar to a soda feldspar. However, Nepheline Syenite has much different origins than soda spars, and as such, is actually much more chemically-complex. generally, nepheline syenite contains a varying blend of nepheline, iron minerals, soda feldspar and potassium feldspar, as well as silica, alumina, and calcium. Nepheline syenite is a low silica, high soda and high alumina mineral. Its high alumina content strengthens glass, and the high soda makes it a great flux.
When added to clay, Nepheline Syenite can reduce crazing tendencies. It can also significantly lower the fusing temperature of traditonally-high temperture claybodies, such as porcelain. Nepheline Syenite has beome a mainstay in the ceramics industry over the years, where it is used as a popular filler/claybody constituent in tile and industrial-garde porcelain production.
Added to glazes, Nepheline syenite increases the firing range of low-fire and mid-range glazes. Nepheline Syenite can, however, incrase crazing in glazes due to its high thermal expansion.