Labradorite. Labrador
spar is a felspar, crystallising in the triclinic system. It is usually
translucent rather than transparent, and by transmitted light appears
of a gray colour. Owing chiefly to a peculiarity in its intimate or
minute structure, which resembles a complex system of gratings,
labradorite often shows magnificent chatoyant reflections of brilliant
blues, sea green, orange, puce, amber, and peach-blossom hues, in fact,
a coloured metallic sheen. It should be cut with a nearly plane or but
slightly convex surface. It occurs, associated with hypersthene and
amphibole, of fine quality in the island of St. Paul, and in large
masses on the coast of Labrador ; also in Finland, Volhynia, the United
States and Queensland. Labradorite has the hardness 6, and the specific
gravity 2.7 to 2.75. In 100 parts it contains :
In some specimens there is less lime, but instead, a small percentage of potash and magnesia.
Moonstone or Adularia. This
is a variety of felspar, or rather of that species of mono-clinic
felspar called orthoclase or orthose. Moonstone is found at St.
Gothard, and very abundantly in Ceylon. It differs from ordinary
orthoclase in the remarkable pearly reflection of light which it
exhibits in certain directions. The most esteemed specimens are those
in which the chatoyancy has a distinctly bluish hue. Some varieties are
nearly opaque ; a chocolate-coloured sort has also been found. The
bluish stones only possess a market-value. The hardness of moonstone is
6, and its specific gravity almost invariably 2.58. It contains in 100
parts :
with traces of lime, and magnesia.
