The Spinel Ruby and Balas Ruby

In connection with the oriental ruby two other productions of quite a different nature must be described, namely, the spinel ruby and the balas ruby.

The first is generally a very vivid poppy red; the second of a violet rose, or a vinegar rose; but there is no absolute rule for their colour, since Pegu furnishes white and violet-white spinels; and specimens have been brought from Aker in Sudermania which are of a bluish gray.

Spinels are brought also from Ceylon and other oriental countries; everywhere they are found in the beds of torrents, in the midst of alluvial deposits.

The primitive form of the crystals of spinel ruby is octahedral, like that of the diamond; this characteristic suffices to distinguish immediately the spinel or balas ruby from the oriental ruby, since the crystals of the latter present the form of six-sided prisms.

The composition of the spinel ruby and balas ruby differ essentially from that of the oriental ruby, the latter being a corundum formed nearly exclusively of alumina, while in the former only 70 parts in 100 are alumina, and the remainder chiefly magnesia. The colour, moreover, is in part due to the oxide of chromium, a substance of which the oriental ruby does not contain the slightest trace.

In a scientific point of view the balas ruby does not differ from the spinel; and many special works confound the two completely. But in commerce the stone called Balas has a value very much below that of the spinel.