Leucite- and Feldspar-Bearing Systems
Nephelinites have been considered to be the most perplexing group of igneous rocks by Bailey (1974). Such rocks predominantly contain nepheline and augite with other accessory minerals. They are usually associated with rocks of melteigite–ijolite–urtite series in close proximity to either leucite-bearing mafic lavas, or carbonatites. Sometimes, they are also observed as a highly fractionated group of rocks derived from lavas of alkali basalt –phonolite series; in such cases, sanidine becomes an important phase in addition to augite and nepheline.