Nepheline

Formula: Na3K(Al4Si4O16)

Colour: White, grey, yellowish

Lustre: Vitreous, Greasy

Hardness: 5½ – 6

Specific Gravity: 2.55 – 2.66

Crystal System: Hexagonal

Member of: Feldspathoid Group: A family of rock-forming minerals consisting of aluminosilicates of sodium, potassium, or calcium and having too little silica to form feldspar. There is considerable structural variation, so it is not a true group. Feldspathoids take the places of feldspars in igneous rocks that are undersaturated with respect to silica or that contain more alkalis and aluminium than can be accommodated in the feldspars. Feldspathoids commonly occur with feldspars, and also with amphiboles, olivine, and pyroxenes, but never with quartz or other polymorphs of silica.

Name: From the Greek “nephele” for “cloud” since it turns cloudy when treated with strong acid.

Type Locality: Mount Somma, Somma-Vesuvius Complex, Naples, Campania – Italy

Dimorph of: Trinepheline