The Oriental emerald or green sapphire does not approach the beryl or
true emerald in depth of color, but because of its superior hardness
and brilliancy, added to its extreme rarity, it is the most valuable of
green gems. The Oriental amethyst or purple sapphire sometimes reflects
a red color by artificial light, and is valued highly as a gem stone;
the common amethyst is softer, less brilliant, and loses by artificial
light.
The various other colored sapphires, such as yellow or Oriental topaz,
light green or Oriental aquamarine, greenish-yellow or Oriental
chrysolite, and aurora-red or Oriental hyacinth, are all valuable as gem
stones when they are pure, well cut, and have pronounced colors—in
fact, the name Oriental is given to distinguish the corundums from
the less valuable minerals of the same colors which they resemble,
but which they greatly surpass in beauty and value because of their
brilliancy and superior hardness.