Nephelinebearing

Nepehelinebearing is a descriptor used in geology and mineralogy to refer to rocks or mineral assemblages in which nepheline is a prominent and stable constituent. Nepheline is a feldspathoid mineral with a formula commonly written as Na3K(Al4Si4O16). It crystallizes in the hexagonal system and is typically colorless to pale, occurring in silica-undersaturated, alkali-rich magmas.

In mineral and petrological terms, nepheline-bearing rocks form in environments with low silica activity and high alkali content. Nepheline is a characteristic phase of alkaline rocks, especially those that are peralkaline. Common nepheline-bearing rock types include nepheline syenite, phonolite, and certain carbonatites and other alkalic intrusions. The mineral assemblage often includes alkali feldspar, leucite, melilite, and minerals such as aegirine-augite or magnetite, with nepheline serving as a key indicator of silica undersaturation.

Geological significance rests on the use of nepheline as an index mineral for classifying alkaline, silica-undersaturated rocks. The presence and proportion of nepheline help distinguish nepheline-bearing rocks from silica-saturated granitoids and feldspathic rocks. The term is also applied when describing metamorphic or metasomatic rocks that have crystallized nepheline under suitable chemical conditions, though this is less common than in igneous contexts.

Overall, nephelinebearing denotes rocks or assemblages dominated by nepheline, reflecting specific magmatic conditions—namely alkaline, low-silica environments—under which nepheline forms and remains stable.