I.
ADULARIA.
This stone is so called from Adula, the
Latin name of Mount St. Gothard, as the best kind is obtained there,
and particularly from that part called the " Monte della Stella."
Adularla
belongs to the felspars, of which it is the purest kind. Its crystals
have one of the facets deeply indented in the direction of the greater
diagonal. Their primitive nodus is an oblique prism with
rhomboidal sides, whose base is an oblique angled parallelogram ; the
secondary forms present an oblique prism with four facets, a large
rectangular prism, a tablet with six facets, and a rectangular prism
with six facets.
Masses
of rough adularla are found in which there frequently exist double
crystals, and yet in this state of perfect union they have different
degrees of hardness. Some also are opaque, others translucent or clear.
This union of massed crystals causes the iridescence which often
distinguishes those found in Italy, France, Germany, Norway, America,
and the Isle of Ceylon.
That
which comes from the Monte Stella is transparent, and has whitish
reflections tinted with green and blue ; some pieces shine with pearly
light. Others
