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Nepheline Syenite: Nepheline syenite is a medium to coarse-grained, light- to medium-gray, igneous rock that is composed predominantly of a silicate mineral called orthoclase and has a granite-like appearance. It may be distinguished from granite by little or no quartz content. Used in Glass and Ceramics: Nepheline syenite is a light-colored, quartz-deficient feldspathic rock made up of mostly soda and potash feldspars and nepheline. In glass and ceramics, nepheline syenite, like feldspar, provides alkalis, which, as a flux, lower the melting temperature of a glass or ceramic mixture, prompting faster melting and fuel savings. In glass, nepheline syenite also supplies alumina, which gives increased resistance to scratching and breaking, improved thermal endurance, and increased chemical durability. -- Excerpts from: Arkansas Geological Survey Website, 2002; and USGS Minerals Yearbook, 1999 |