GEMS certain stones, which, on ac count of their hardness, transparency, and beauty, when cut and polished, are highly esteemed, and, from their small size and scarcity, are valued at very consi derable price. The gems have been plac ed among the siliceous fossils, as in some measure allied with them in external cha racters; and silex was supposed to be their principal ingredient. Bergman first sheav ed the error of this opinion, and proved, by analysis, that in the emerald, sapphire, topaz, ruby, and hyacinth, argil predomi nates ; their other constituent principles, as discovered by his analysis, being silex, lime, and oxide of iron. Still, however, the old prejudice prevailed, and they have been generally ranked by mineralogists under the siliceous gems.
The specific distinctions of these fossils were not less osbcure; they were perplex ed by the distinctions of the jewellers, drawn from very vague notions : the co lour, in particular, being the property in which the gems differ most obviously, and which frequently gives them their mer cantile value, served as a ground of dis tinction : hence the ruby, the sapphire, and the topaz, were considered as differ ent, though essentially the same. Another circumstance, added to the confusion thus introduced, was, that other fossils, bearing a resemblance to these gems, had been classed with them ; but, being inferior in lustre, transparency, and hardness, in or der to distinguish between them, the epi thet oriental was applied to those which were most perfect ; and, by this contri vance, fossils were classed under one name, and regarded only as varieties of one species, which were totally different. The Oriental and the Saxon topaz, for ex ample, were regarded under this point of view, or as varieties of one species, to which the common name of topaz belong ed, though they are fossils altogether dis tinct. From these two circumstance s,fos
sils were separated, which ought to have been associated, and others were connect. ed, which were specifically different ; and it has required much mineralogical discus sion to disentangle the perplexity, and establish the proper species.
Romi de l'Isle ,threw the first ray of light on this subject, by disregarding the colour, and attendingrather to the form of crystallization ; in consequence of which: he arranged together the principal gems named oriental, under the title of the ori ental ruby. Werner also has placed them under one species, to which he gives the name of sapphire. Ilauy has adopted the same arrangement, distinguishing the spe cies by the name of telesie; and, more lately, Bournon has still farther extended the relations of these fossils, by connect ing them with the corundum, a fossil which had been brought from India, and which, analysed by Klaproth, was found to be composed principally of argillaceous earth. This, having in general little transparency or lustre, Bournon names imperfect corundum ; while the other va riety, possessing these qualities, and com prising the oriental gems, is distinguished by the appellation of perfect corundum : these arrangements have received the sanction of chemical analysis. The skill •of Klaproth, of Vauguelin, and Chenevix, has been exerted in investigating the corn po sition of these fossils, and they have prov ed to be argil nearly pure. See Dramosn,