principally the primitive; and is found in Dauphine, the Pyrenees, Gothard, Saxony (Thum), Norway, &c.
This
mineral takes a very high polish, particularly those specimens from
Dauphine, but has hitherto, on account ot its scarcity, not found much
application in jewelry, but will hereafter be a great acquisition, as
it may be used for rings, pins, and other small ornaments
FELSPAR.
The
varieties of this mineral are mostly crystallized, and in very numerous
forms; but they are all distinguished by two great characters, which
are, the foliated structure and peculiar lustre; the principal form is
an 'oblique prism with unequal sides. Felspar scratches glass and is
scratched by rock crystal; its streak-powder is white; it has a
specific gravity of 2.5 to 2.6; before the blowpipe it fuses with
difficulty; on charcoal it becomes vitreous and white; fuses with
difficulty on the edges to a translucent white etiamel; acids have no
effect upon it; it consists of potash, alumina, and silex.
ADULARIA.
This
mineral occurs in crystals (oblique prisms and rhom-boidal faces),
crystalline fragments, and solid masses; its fracture is uneven; it is
translucent on the edges; has double refraction of light; the lustre is
vitreous and pearly, more especially when cut and polished; it throws
out greenish and bluish-white chatoyant reflections from the interior;
it cleaves in two directions; the crystals often present the hemitrope
form, wThich in polished specimens becomes obvious from the
different directions of the laminae; its'colors are limpid-white,
greenish, grayish, and bluish, frequently
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