The nepheline syenite on Stjernøy is characterized by silica deficiency and excess alumina. Alkali feldspar and nepheline are the dominant minerals, and femic minerals constitute less than 5 per cent of the rock.
The geochemistry of the rock is discussed, and attention is drawn to the low concentrations of Nb, Li, Zr, Y, Nd, La, U, and Th. All these elements are often concentrated in alkaline rocks. Low concentrations of Rb, Cs, Pb, and Tl, with high concentrations of Sr and Ba may reflect conditions at the site of magma formation but may also reflect partition of elements between the crystallizing magma and a gas phase.