heating
them so that they become colourless. Of other gems with which it might
be confused Diamond is the only one which will scratch it. Zircon is
the only one which equals it in density, and Zircon so far exceeds all
other gems in this respect that it is easily distinguishable.
Oriental
Chrysolite is Corundum of the colour of Chrysolite or Olivine. This is
not a very rare tint. It is distinguished from ordinary Chrysolite by
the greater hardness.
Oriental
Emerald is an emerald-green form of Corundum, and is extremely rare.
The New South Wales Sapphire deposits have produced a relatively large
number. In value it is between the Sapphire and Ruby. It is harder than
Emerald, more strongly dichroic, of higher specific gravity, and is
sometimes fluorescent.
Oriental
Topaz includes several yellow shades of Corundum, and when of fine
reddish yellow colour is of about the same value as Sapphire. It is
distinguished from Topaz by higher specific gravity and greater
hardness.
Oriental Hyacinth is a reddish brown variety. It is also known as Vermeille Orientale.
Oriental
Amethyst, also called the Purple—or Amethyst— Sapphire, is very close
in colour to the common Amethyst, but it shows a much greater range of
colour than Amethyst does, and in fact may vary from a slightly purple
red to a blue with a slight tint of red in it.
2.
The second mineralogical variety is Common Corundum. It is less
transparent than the first variety. The colour varies from dull blue to
grey and from a rich smoky brown to black. It often has a very marked
adamantine lustre, and the brown asteriated form, when cut en cabochon,
