Nepheline syenite: for glass and ceramics industry

Nepheline syenite (foid, feldspathoid, feldspar representative)

Feldspar representatives (foids), such as nepheline, are formed when the silicon in the residual melt runs out during feldspar formation. Rocks with feldspar representatives therefore basically contain no (very little) crystalline quartz.

NS is a raw material rich in Na2O, it lowers the melting point in glazes because the mineral easily forms eutectic mixtures, or formulated differently: It lowers the melting temperature in the melt because it reacts with the quartz it contains and has a wide melting interval 1060-1230°C. NS is also a raw material saver because, compared to feldspar, less quantity of it is needed in the compositions (melts) to produce the desired results. It thus acts as a high quality feldspar substitute in melts and ceramic bodies.
In ceramic bodies, it serves as a leavening agent before firing, as a flux in sanitary ceramics, in floor and wall tiles, and in hard stone bodies. Again, the advantage is that NS has a lower melting point than sodium feldspar and therefore requires a shorter firing time and less energy input.

However, each industry has different requirements for nepheline syenite quality. Selection criteria for this, in addition to the price of the material, can be its color, iron oxide content, grading curve, and other factors. 

There exist worldwide, depending on the "impurities" in the mineral, very many color variations, from white, yellowish, gray, anthracite, green, blue, beige to brown, of nepheline syenite. The color spectrum of our raw nepheline syenite, due to hematite impurities, is in the golden yellow-beige-brown range.

The Mohs hardness of the NS is between 6 and 6.5, the bulk density between 60-1100 kg/m³, the specific gravity at 2.5-2.7 g/cm³ and the SiO2 content between 60-70%.