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Ch. 3: Precious Gem stones in 1886

Ch. 3: Precious Gem stones in 1886 Page of 19 Ch. 3: Precious Gem stones in 1886 Text size:minus plus Restore normal size   Mail page  Print this page
PRECIOUS STONES.                                    603
optical properties of these stones are such that they are evidently individual or parts of individual crystals, and not agglomerations of crystals or groups fused by heating. In my opinion these artificial rubies were produced by a process similar to that described by Fremy and Feil (Comptes Eendus, 1877, p. 1029), by fusing an aluminate of lead in connection with silica in a siliceous crucible, the silica uniting with the lead to form a lead glass and liberating the alumina which crystallizes out in the form of corundum in hexagonal plates, with a specific gravity of 4.0 to 4.1, and the hardness and color of the natural ruby, the latter being produced by the addition of some chromium salt. By this method rubies were formed, which, like the true gem, were decolorized temporarily by heating.
It is not probable that these stones were formed by Gaudin's method {Comptes Eendus, XIX., p. 1342), by exposing amorphous alumina to the flame of the oxyhydrogen blowpipe, and thus fusingit to a limpidfluid, which, when cooled, had the hardness of corundum, but only the specific gravity 3.45, much below that of these stones. Nor is it ab all likely that they were produced by fusing a large number of natural rubies or corundum of small size, because by this process the specific gravity is lowered to that of Gandhi's product. The same also holds good of quartz, beryl, etc.
The French syndicate referred the matter to M. Friedel, of the Ecole des Mines, Paris, supplying him with samples of the stones for examination. He reported the presence of the round and pear-shaped bubbles, and determined the hardness and specific gravity to be about the same as of the true ruby. On analysis he found them to consist of alumina, with a trace of chromium for the coloring matter. The cleavage was not in all cases distinct, and the rough pieces given to him as examples of the gem in its native state had all been worked, so that nothing could be learned of their crystalline structure. When properly cut according to axes, they showed the annular rings. The extinction by parallel light was not always perfect, which he believed to be due to the presence of the bubbles. He states that he himself has obtained small red globules with these inclusions by fusing alumina by oxyhydrogen light; and, although having no positive evidence, he believes these stones to be artificially obtained by fusion.
On the receipt of M. Friedel's report the syndicate decided that all cabochon or cut stones of this kind shall be sold as artificial, and not precious gems. Unless consignments are so marked the sales will be considered fraudulent, and the misdemeanor punishable under the penal code. All sales effected thus far, amounting to some 600,000 or 800,000 francs, shall be canceled, and the money and stones returned to their respective owners.
The action taken by the syndicate has fully settled the position which this production will take among gem dealers, and there is little reason to fear that the ruby will ever lose the place it has occupied for so many centuries.
Ch. 3: Precious Gem stones in 1886 Page of 19 Ch. 3: Precious Gem stones in 1886
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US Geol. Surv. 1886. Gemstones, Metals.
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