Nepheline (), also called nephelite, is a rock-forming mineral in the feldspathoid groupa silica-undersaturated aluminosilicate (Na<sub>3</sub>KAl<sub>4</sub>Si<sub>4</sub>O<sub>16</sub>) that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites. It is used in glass and ceramic manufacturing and other industries, and has been investigated as an ore of aluminium.
Description and properties
thumb|left|Grayish-white nepheline crystals with dark [[schorlomite from Bou-Agrao Mount, Tamazeght complex, High Atlas Mountains, Morocco. Size: |204x204px]]
Nepheline crystals are rare and belong to the hexagonal system, usually having the form of a short, six-sided prism terminated by the basal plane. The crystals appear to have more symmetry than they actually possess, but unsymmetrical etched figures produced artificially on the prism faces indicate that the crystals are hemimorphic and tetartohedral, the only element of symmetry being a polar hexad axis. Nepheline is found in compact, granular aggregates, and can be white, yellow, gray, green, or reddish. Its hardness on the Mohs scale is 5.5 to 6, and its specific gravity 2.60–2.65. It is often translucent with a greasy luster. For this reason, a clear crystal of nepheline becomes cloudy when immersed in acid.
Uses
Because of its high alumina content, iron-free nepheline is valued for use in glass manufacturing in place of feldspar. Most of the nepheline used for this purpose comes from Ontario. Nepheline produced as a byproduct of apatite mining in the Kola Peninsula has found uses in ceramics, leather, rubber, textiles, wood, and the oil industry. It can be used as a filler in paints, plastics, foam rubber, and sorbent. Nepheline of Kiya Shaltyr deposit (Kemerovo Region, Russia) is also used as a raw material for aluminium manufacturing.