It is commonly used as a felsic rock. An excellent basis for glazing in the conical range 4-6, it is also used in some 10 conical glazes. Nepheline syenite is anhydrous sodium alumino silicate. Excellent source of soda. Although similar to feldspar in its chemistry, minerally it is a mixture of igneous rocks of nepheline, microcline, albite and secondary minerals such as mica, hornblende and magnetite. Like feldspar, nepheline syenite is used as a flux in tiles, sanitary ware, porcelain, and glass and semi-glass objects. It contributes to high alumina without the presence of associated free silica in its raw form and flows to form silicates with free silica in the bodies without contributing to the free silica itself. This stabilizes the expansion curve of the burning object. It is an excellent filler and melter for tiles, especially for fast burning. Nepheline syenite is valuable in batches of glass for achieving the lowest melting temperature while serving as a source of alumina. Since nepheline syenite can be slightly soluble, it can be responsible for changes in hardness during aging (although many other factors can also contribute to this). It may be more difficult to keep tile bodies de-bulged with nepheline syenite than with feldspar. However, where you may notice the solubility of nepheline most is in glazes that have large percentages and can solidify over time and adding more water to thin out the slurry can spoil the performance of the application.