A complex rock made up of nepheline (primarily), albite and microcline used in ceramic glazes and clay bodies to initiate or promote fusion. It is mined in Southern Ontario, northeast of Peterborough. A 3:1 mixture of nepheline syenite and silica can be used to substitute for soda feldspar such as Minspar 200. Its slight solubility can lead to hard panning in glazes; correct with epsom salts.
For more information on nepheline syenite, see the Digitalfire.com Reference Library of ceramic materials.