# Precious Stones/Chapter 5: Artificial Formation of Precious Stones

CHAPTER V.
ARTIFICIAL FORMATION OF PRECIOUS STONES.
A clear distinction must be made between the imitation of a precious stone and its actual reproduction or formation by artificial methods. In the former case we simulate the appearance of the natural substance by means of some product or preparation, which may be (and generally is) widely different in chemical composition and even in many physical properties. In the latter case we form the very mineral which Nature has formed, endowed with all its chemical and physical characters, but not necessarily produced by processes identical with those of Nature. A few examples of the true reproduction of precious stones will serve to explain the distinction pointed out with sufficient exactitude.
Take the case of the ruby and sapphire, varieties of crystallized alumina or corundum. If, by the aid of the intense heat of the oxyhydrogen blowpipe pure alumina, with traces of chromium oxide or other colouring oxide, be fused, we get a sapphire or ruby glass, having a hardness and density much less than those belonging to crystals of alumina. But by prolonging the time of cooling or by producing the alumina from some of its compounds during the heating, a portion of the product will crystallise in forms identical with those of the natural stone, and having the density of 4 and the hardness 9. For some time the specimens made were small in size and poor in colour and brilliancy, but the product was identical with native corundum. Now there have been, among the large numbers of artificially-prepared rubies, some of several carats in ​weight which can be distinguished from the natural stones only by a close examination with the microscope. It is then observed that the artificial rubies contain cavities of a different outline and nature to those which occur in the rubies made in nature’s laboratory. These cavities are more or less spherical or pear-shaped in the artificial ruby and their walls are curved; in the natural stone the cavities are really negative crystals while their walls are angular. It was the French chemist Frémy who first made small rubies artificially, but subsequent workers, by employing larger quantities of material, modifying the ingredients taken, and allowing the fused product to cool more slowly, have achieved greater success. The exact way in which the so-called re-constituted rubies are made is not known, nor can absolute reliance be placed upon the descriptions which have been given of other methods of ruby-formation. The red spinel has also been made artificially, of good colour, and in large crystals. The spinel is a compound of alumina and magnesia, and by the aid of a substance such as boracic acid, which acts as a solvent for the constituents of spinel, but which volatilizes at very high temperatures, crystals of spinel having considerable dimensions, good colours, and the hardness of 8, have been obtained by several chemists. These stones, having been cut and polished, could not be distinguished by any test from the natural gems. Another method of operating, by which rock crystal and a considerable number of hard transparent and beautiful compounds of silica have been made, consists in causing two substances to act upon each other when both are in the state of vapour, sometimes with the aid of the vapour of water as a decomposing agent, and sometimes without. By the reaction of fluoride of aluminium and. boracic acid, fluoride of boron and alumina are produced, the latter crystallizing in colourless rhombohedra of white sapphire, or even, when chromium is added, taking the colours of ruby and blue sapphire. Similarly treated at a very high temperature in a lime crucible, the fluorides of aluminium and glucinum have been made ​to yield distinct crystals of chrysoberyl. It is probable that in Nature the formation of gem-stones has occurred in the presence of water, and under very great pressure continued for a long time. Indeed, it may be concluded that the agency of a very high temperature has not been generally at work, but that the important elements in the production of natural crystals have been time, mass, and pressure.
Chemists have devoted much time and skill to devising methods for producing diamonds. These methods have rarely been successful, but M. Henri Moissan has really made a number of small—very small—diamonds by causing carbon to dissolve in molten iron at the high temperature of the electric furnace and then, by sudden cooling of the metallic mass, causing the formation of a rigid shell and so producing great pressure in the interior: the iron mass treated with acid left a residue containing small diamond crystals: by slow cooling graphite only was formed.
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