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In spite of all the discussions that have arisen on this subject, and the great number of classifications presented by different authors who have occupied themselves with the question, there does not exist, and there cannot exist, any general and natural classification of precious stones. The reason is very simple: these substances being what we may call particular cases in nature, it is not possible to arrange them in series. By choosing any one of their general characteristics, crystalline form, refraction single or double, composition, or commercial value, &c., the geometrician, the physicist, the chemist, and the merchant can easily establish a classification answering more or less completely to their special end; but this is not a natural classification.
Without discussing or criticizing the different methods proposed, we shall adopt a classification based upon chemical composition.
If there should be placed upon a table a specimen of every kind of precious stone known at the present day, it would be possible to separate them immediately, according to their chemical composition, into three perfectly defined groups.
The first comprises a single precious stone, the diamond. Its constituent principle is carbon.
The second includes the sapphire, the ruby, the topaz, the amethyst, the emerald, &c.--stones of which alumina is the base.
The third comprises stones whose base is silica--the opals, the agates, &c.
Carbon, alumina, silica: this is the order of importance of the three substances which enter essentially into the composition of precious stones; and in this order we shall arrange the chapters devoted to the history of all the gems which each division includes.
But before studying these groups, two descriptive terms applied to precious stones should be explained, the terms Oriental and Occidental.
Originally these words were applied in their literal sense; but at the present time they are retained in commercial parlance, not to indicate the regions from which the precious stones are brought, but simply to establish between stones of the same name a comparative value. The most precious variety of any precious stone is called Oriental, and the inferior variety Occidental, whatever may be the countries in which they are found. |
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Precious Stones Guide Vol 2
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