NEPHELINE

also called nephelite, or eleolite the most common feldspathoid mineral, an aluminosilicate of sodium and potassium (Na3KAl4Si4O16). It is sometimes used as a substitute for feldspars in the manufacture of glass and ceramics. Nepheline is the characteristic mineral of alkaline plutonic rocks, particularly nephelinesyenites and nephelinegneisses. It occurs in beautiful crystal form with mica, garnet, and sanidine feldspar on Monte Somma, Vesuvius, Italy. For detailed physical properties, see feldspathoid (table). Carnegieite is synthetic, high-temperature nepheline. Kaliophilite is the high-temperature form of kalsilite, the potassium-rich variety of nepheline. Kaliophilite is unstable at normal temperatures and rarely occurs in nature.