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PRECIOUS STONES.

But the spinel owns other hues which labour under no such disadvantages. There is a brilliant aurora red, and a whole suite of passage hues, between indigo and puce, which stand alone for curious beauty. And to these may be added steel-grey, slate and sky-blue, without exhausting the colours offered by the spinel.

The red varieties of the spinel are generally spoken of as "spinel ruby" and "balas ruby," those designated by the latter name being inferior in colour and brilliancy, and less like the true ruby; but, chemically and physically, there is no sharp distinction between them. "Rubicelle" is a term applied to orange and flame-coloured spinels, those that are violet and purple being called "almandine" spinels.

Spinels fit for use in jewellery come from many localities. Of these the chief are in Burma, Siam, and Ceylon; also in the United States, in New York, and New Jersey, but the fine large red spinels come exclusively from India; several of these, weighing, when properly cut, as much as 25, 72, 81 carats, have recently found their way to Europe. One rose-coloured specimen weighed as much as 150 carats, but being too pale was sold for no more than £80. An unusually large and fine crimson spinel or spinel-ruby, weighing 491/64 carats, from India, proved to have the specific gravity 3·582, while its index of refraction was—for the red ray, 1·711, for the yellow ray, 1·714 and for the blue ray, 1·719. Its hardness scarcely exceeded that of the red garnet, but the tests of specific gravity and refraction sufficed to show that it was a true spinel. A spinel ruby of rich colour is seen probably to the best advantage when step-cut; the paler hues often look well brilliant-cut. A border of small diamonds enchances the colour and beauty of a spinel.

The spinel crystallizes in the cubic or monometric system, a regular octahedron being its most common form. Some of the natural crystals of spinel are so perfect in shape and polish that they are quite fit for ornamental mounting without further preparation. The hardness of this gem is 8, while its specific gravity