SAPPHIRE-MINING INDUSTRY OF ANAKIE 255
showing
the familiar triangular striations on the base, are not uncommon. In
some instances the basal parting planes are so fine that they give a
moonstone-effect in the polished stone. Stones of the star-sapphire
type, showing the phenomenon of " asterism," also occur.
The
hardness of the Anakie sapphires is stated to be somewhat variable.
Lapidaries find in cutting the stones that some portions are more
difficult to cut than others, and they have repeatedly stated that in
some specimens the hardness is greater than 9, which is the degree of
hardness of typical corundum.
The
specific gravity of many specimens which have been examined has varied
from 4 to 4-05. The colour is variable, and the following eight
varieties have been observed: sapphire (blue), " oriental amethyst"
(purple), " oriental ruby " (red), " oriental peridote " (green), "
oriental chry-soberyl" (yellowish green), " oriental topaz" (yellow), "
oriental cat's eye " (smoky), and " oriental moonstone" (pearly).
The
lustre of the clear stones is stated to be " almost adamantine," but in
the coarser translucent varieties it may be opalescent, bronzy, milky,
pearly, or silky. Opaque varieties are usually black, but sometimes
also brownish-black, dark blue, light blue, and greyish-white.
In
some of the stones foreign mineral matter has penetrated the parting
planes, in some instances rendering the stone opaque. In other
instances a blood-red colour may be seen along certain directions, due
to the deposition of films of haematite. Magnetite occurs as inclusions
in some specimens, sometimes in the form of microscopic crystals. In
several specimens of deep-green sapphire, magnetite was observed in
dusty masses, and in one crushed specimen it was readily detected both
with the blow-pipe and magnet.
Geological Features
The
oldest and most widespread rocks of the district are granites,
syenites, gneisses, schists, and slates. Pegmatite, porphyry, and
felsite occur abundantly as intrusions traversing the granites and
gneisses in all directions.
