Nepheline syenite is a white to light grey medium-grained igneous rock. It consists mostly of soda feldspar, nepheline and potash feldspar, accessory magnesium and iron-rich minerals. The Canadian nepheline syenite industry began in 1932 when claims were staked on Blue Mountain near Peterborough, Ontario, where it is still produced. Persistent and lengthy efforts in technical and market research and development were necessary to establish this industry. Canada was the first country to develop the use of nepheline syenite as a raw material for glass, ceramic and filler industries and was the world's only producer for many years.
Over the years, nepheline syenite has become preferred to feldspar as a source of alumina and alkalis for glass manufacture. It promotes more rapid melting at lower temperatures, thus reducing energy consumption, lengthening the life of the furnace and improving the yield and quality of glass. The material is used in ceramic glazes and enamels and in fillers in paints, papers, plastics and foam rubber. In Canada, about two-thirds of nepheline syenite is consumed by the glass industry for containers, flat glass, insulating fibreglass and textile glass fibre.
Nepheline syenite is extracted from open pit mines. Ore is hauled to the mill, where it is put through a magnetic separation circuit to remove iron-bearing minerals. The mill produces several grades of nepheline syenite, based on grain size and iron content, to meet a wide variety of markets. Annual shipments exceed 700 000 t.
See also metallurgy.