Nepheline - (Na,K)AlSiO₄

Habit: Typically colorless, white, gray or yellow, but can be many colors. Stout six- or twelve-sided prisms, typically poorly formed; also granular, compact or massive. Vitreous to greasy luster; transparent to nearly opaque, from inclusions or alteration. White streak.

Environment: Characteristic of alkalic rocks as nepheline syenites and gneisses and alkalic gabbros. Also occurs in sodium-rich hypabyssal rocks, tuffs and lavas and pegmatites and as a product of sodium metasomatism.

Etymology: From the Greek word for "cloud," because it becomes cloudy when treated with strong acid.