Book Name Gems and Gem Minerals Author Farrington published 1903

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Farrington Gems and Gem Minerals

Gems are minerals prized for their color, hardness, luster, and, for the most part, transparency. It is generally essential that a mineral to be a gem should excel in at least three of the above-named properties, although a few are superior in only two. Some minerals may, for example, possess desirable color and luster, but, lacking hardness, are little used for gem purposes, because they would become quickly marred when worn. Fluor-spar is an illustration of such a mineral. That a high degree of hardness is not essential, however, to the employment of a mineral as a gem is shown by the extensive use of such substances as pearl, amber, jet, and turquoise, for gems. All of these are easily scratched by ordinary objects. It is to be noted, however, that they are not transparent substances, and that an opaque or translucent substance may endure, without serious injury, scratches which would be fatal to the beauty of a transparent gem. Hardness and color alone cannot, however, make a mineral suitable for gem purposes. This fact is illus­trated by many varieties of corundum, which have a high degree of hardness and good body color, but are not used for gems because not transparent. It is evident, therefore, that no fixed rule can be assigned for the use of a mineral as a gem, the favor or disfavor in which it is held seeming, in many instances, to be a matter of pure caprice.