Nepheline appears to decrease in amount as leucite increases.
The flows from Kibo include nepheline and leucite basanite lavas rich in soda felspars.
leucite, lū′sīt, n. a whitish mineral occurring only in volcanic rocks.
The leucite lavas of Niedermendig contain hayne in abundance.
leucite and nepheline rocks have been found in various parts of the island, especially in the south-west.
They are of trachytic appearance, containing phenocysts of sanidine, leucite, augite and biotite.
In the lava of 1848 leucite was found to reach 44.9 per cent.
They are rich in leucite, but contain also some sanidine and often much nepheline with hauyne or nosean.
The former consist mainly of plagioclase, leucite and augite, while the latter contain olivine in addition.
leucite lavas from which felspar is absent are divided into the leucitites and leucite basalts.