The blue corundum, ranging in color from the lightest blue to deep blue
and black, is the same stone as the ruby, the only difference being in
the color.
The choicest color is the soft velvety blue, approaching the
corn-flower in shade and exhibiting that color vividly by artificial as
well as by natural light.
The deeper-colored stones are known as male, and the light-colored ones
as female sapphires.
Although choice sapphires are rare, a much greater quantity of good and
large stones are to be had than of rubies, and therefore the price of a
large sapphire does not advance in the same proportion as the price of
a large ruby.