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184 PRECIOUS STONES.
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are inferior in hardness, and wanting in the adamantine lustre,
as well as some other characteristics of this precious stone. An attempt has been made to give yellow diamonds a blue tint by means of aniline dye or a certain kind of blue pencil, with a view of enhancing their commercial value, but the fraud is too palpable easily to escape detection. The latter process consists in wrapping the stone in a damp sheet of tissue paper which has been rubbed with powder abraded from a blue pencil, and to prevent detection, the gem is set before it is offered for sale. Counterfeit Diamonds. — There are so many colorless gems
which resemble the diamond that it is quite difficult, if not impossible, for one, not an expert, to detect the spurious from the genuine article. Rock-crystal, colorless varieties of spinel, topaz, emerald, sapphire, beryl, and zircon, have all passed for diamonds. White zircon and phenakite, of all natural counterfeits, come nearest to them in play of colors ; rock-crystal is inferior in lustre. The Novas Minas or white topaz of Brazil, sometimes called the " Slave's diamond," is very hard and brilliant, but lacks the adamantine lustre and iridescence of the true diamond. Various methods are employed to detect counterfeits of this
gem, depending upon its peculiar properties, such as its electrical powers, its single refraction by which it is distinguished from most other precious stones ; but the most decided tests are, probably, those of hardness and specific gravity. The most convenient method of testing the diamond, it has been said, is to submit it to a white heat and then apply the point of a sapphire. If it is genuine, it will undergo the former ordeal without melting, and the latter without being scratched. Mines and Mining. — The uncertainty and hazards attend-
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