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Although of great importance to the chemist, the gemologist is normally not greatly concerned with the chemical composition of gem stones, unless he is interested in their mode of origin, or perhaps in the manufacture of synthetic stones. A knowledge of this subject would be of use if he were interested in the changing of color in certain varieties, although commercially this has been carried out in the past largely on a hit or miss principle. But in general, gem stones are amongst the most stable of substances; they are not easily broken up, and they seldom combine chemically with other matter. They are therefore of more interest to the physicist than to the chemist.
The determination of the individual elements, or combination of elements, which make up a given gem stone would involve the breaking up of the specimen, or even reducing it to a powder, since it would have to be subjected to intense heat and other tests, any of which would render it valueless from a commercial point of view. We therefore depend very little on chemical tests for distinguishing gem stones from one another, but some mention of such tests, which involve the use of a blowpipe, is made in a later chapter. A work on the qualitative and quantitative analysis of minerals should be consulted by the interested reader.
But we can say that the ease with which a stone is fused, if it is fusible, would afford a means of ascertaining its composition. Most gem stones, however, do not respond to this test since they are infusible, or fuse only with great difficulty. Thus diamond, although combustible, is infusible. Ruby and sapphire fuse with the aid of a flux, such as borax, but with difficulty.