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The facial development of crystals of nepheline give no indication of this type of symmetry, and the mineral has been referred to this class solely on the evidence afforded by the etched figures.

These last consist of an intermixture of nepheline or sodalite and alkali-felspar.

Leucite and nepheline rocks have been found in various parts of the island, especially in the south-west.

Some writers held that this mineral has resulted from the decomposition of nepheline; others regard it as a primary mineral.

Vesuvian lava, glass paste with numerous crystals of leucite; others of augite and nepheline porphyritically developed; also small grains of magnetite.