Spinels Explained

Spinel is a mineral somewhat similar to ruby, but as spinel gems are quite different from true rubies, so the mineral spinel is quite distinct from the mineral of the true ruby, which is corundum. In composition spinel is almost wholly a magnesia aluminate, and in hardness is much softer than the ruby, being No. 8, or no harder than the topaz, while the ruby is No. 9.

Spinel occurs in various colors, but the most valuable color is red, called the spinel ruby. From the fact that the spinel so closely resembles the ruby in appearance, it has often been confounded with it, and in cases of fraud spinel is sometimes sold in place of the corundum ruby. In its own sphere, however, the spinel is a beautiful gem, and while never found in very large sizes, has yet been so highly prized that it is found amongst the crown jewels of several nations. The ruby of the "Black Prince," which is shown among the crown jewels of England, is a notable example of spinel.

As a spinel is related to corundum in composition and appearance 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 torn 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 easily 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 Burmah, 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 rubies were equally well known, and the two were probably often confounded. Dr. O. C. Farrington, in his great book, relates as usual some interesting superstitions regarding the spinel. In the middle ages, for instance, it was believed that, "if one touched with this gem the four corners of a house, orchard or vineyard, they would be protected from lightning, storms, and the like."