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of
these is as hard as the ruby, and each differs sufficiently from the
ruby in its refractive powers, or specific gravity, to make
distinction easy.
Rubies
were known to the ancients, being mentioned in the Bible in Proverbs
and Job. The Greeks and Romans ascribed to the ruby the power of giving
light in the dark, and the Hindoos describe the abodes of their gods as
thus lighted. The ruby was much worn as an amulet, being supposed to
protect the wearer against plague, poison, and evil spirits. It was
also thought that it would turn dark if its owner were in danger, and
would not regain its color until the peril was over. The Burmese
believe that the ruby ripens like fruit. The crude are colorless;
thence they grade yellow, green, blue, red.
The
ruby is usually cut in the form of the brilliant, like the diamond,
but sometimes the step cut is advantageously employed. The native
gem-cutters of India do not cut facets on their rubies, but simply
round and polish them.
Blue,
precious corundum, or sapphire, is more abundant than the red or ruby.
Like the red, the blue color seems to be due to a content of chromium,
since in the artificial crystals already mentioned as produced by
Fremy, both colors occur at times in the same crystal. This occurrence
of two colors in single crystals is also found in Nature, some being
red at one end and blue at the other; or, perhaps what is more
frequent, the center of the crystal may be yellow and the exterior
blue. This coloring is not uncommon among the Australian sapphires, and
unique gems are obtained by cutting them so as to show the two colors.
Bauer describes a figure of Confucius carved from a sapphire, of which
the head is white, the trunk and arms blue, and the legs yellow. The
color of sapphire most highly prized is that known as cornflower-blue.
The cornflower (Centaurea cyanus) is also known in this country
by the name of " bachelor's button," and excellently typifies the true
sapphire color. Other shades of blue which occur in the sapphire, are
indigo-blue, smalt-blue, berlin-blue, and greenish and grayish blues.
The sapphires of darker colors are usually known as male and those of
lighter colors as female sapphires. In addition to possessing the true
corn-flower blue color, the best sapphires should exhibit a velvety
sheen, the value of the stone being greater the more perfect this
character.
As
already noted, sapphire is somewhat harder than ruby, and it is also
somewhat heavier. The Montana sapphires are said to be especially hard.
Sapphires have at the present time not over half the value of a ruby
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