iv., Part i., p. 999); olivine and augite (Mitscherlich and Berthier, in the
'Annales de Chimie et de Physique', t. xxiv., p. 376). Notwithstanding the
greatest possible similarity in crystalline form, and perfect identity in
chemical composition, existing, according to Gustav Rose, between augite and
hornblende, hornblende has never been found accompanying augite in scoriae,
nor have chemists ever succeeded in artificially producing either hornblende
or feldspar (Mitscherlich in Poggend., 'Annalen', bd. xxxiii., s. 340, and
Rose, 'Reise nach dem Ural', bd. ii., s. 358 und 363). See also, Beaudant,
in the 'Mem. de l'Acad. des Sciences', t. viii., p. 221, and Becquerel's
ingenious experiments in his 'Trait de l'Electricite,' t. i., p. 334; t.
iii., p. 218; and t. v., p. 148 and 185.
These minerals constitute the main constituents of granite, gneiss, and mica
schist, of basalt, dolerite, and many porphyries. The artificial production
of feldspar and mica is of most especial geognostic importance with
reference to the theory of the formation of gneiss by the metamorphic agency
of argillaceous schist, which contains all the constituents of granite,
p 269
potash not excepted.*
[footnote] *D'Aubuisson, in the 'Journal de Physique', t.
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