Nepheline Syenite

Nepheline syenite is a holocrystalline plutonic rock that consists largely of nepheline and alkali feldspar. The rocks mostly pale colored, grey or pink. In general appearance they are not unlike granites, but dark green varieties also known.

The chemical peculiarities of the nepheline syenite well marked. They are exceedingly rich in alkalis and in alumina with silica varying from 50 to 56%, while lime, magnesia and iron are never present in great quantity, though somewhat more variable than the other components.

The rock is holocrystalline, generally equigranular, equidirectional, and gross with grain size of 2 mm to 5 mm. In certain rare cases, the rock contains alkaline feldspar phenocrysts of 2 cm to 5 cm in length and 5 mm to 2 cm in thickness. The phenocrysts demonstrate orientation and eventually show cumulative texture.