All the upper part of the mountain is composed of a pumiceous tufa, rich in sanidine and of a characteristic greenish colour.
They are of trachytic appearance, containing phenocysts of sanidine, leucite, augite and biotite.
They are rich in leucite, but contain also some sanidine and often much nepheline with hauyne or nosean.
sanidine, san′i-din, n. a clear glassy variety of orthoclase.
It is remarkable for the large crystals of sanidine (glassy felspar) which it contains, and has a rude columnar structure.
(c.) Phonolite (Clinkstone) is a trachytic rock, composed essentially of sanidine, nepheline, and augite or hornblende.
Trachyte from Hungary; felsitic paste with crystals of hornblende and sanidine, and a little magnetite.