As
spinel is related to corundum in composition and appearance so it is
also often found associated with it in nature. The gem gravels of
Ceylon, Siam, Australia, and Brazil contain spinel rubies, and the true
corundum rubies side by side, but the commercial source of spinel
rubies is now almost entirely a locality called Badakschan, in
Afghanistan, on the banks of the Oxus. According to a Persian tradition
these mines were first disclosed when the mountain was rent in twain
by an earthquake.
Besides
the ruby spinel the mineral occurs in several other colors, which may
be used as gems, viz.: red, orange, green, blue, indigo, and also black
and white. Colorless spinels are occasionally passed in cases of fraud
as diamonds, but the deceit may be readily detected.
While
the mineral spinel may be used as a gem in all the colors in which it
occurs, the only shades which are abundant enough to deserve special
notice, aside from the red, are the blue and black. Blue spinel
resembles the sapphire in color, although it is somewhat paler. It
comes chiefly from Ceylon and Bur-mah, where it is found with the ruby
spinel. The black spinel is known as Ceylonite and comes also from Ceylon.
In ancient times spinel rubies and corundum
