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CHAPTER VII.
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THE EMERALD.
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HE Emerald, from a mineralogist's point of view, belongs to a class of stones altogether different from that which embraces the precious stones already described, inasmuch as it is essentially a mineral silicate, consisting largely of the substance known to chemists as Silica. The silica is itself an oxide of an element termed Silicon. In the Emerald the silica is combined with the oxides of two metals—one of them being aluminium, the basis of the Ruby and Sapphire ; while the other is an exceedingly rare metal, known as glucinum or beryllium. The former name is derived from the sweet taste of some of its compounds— from the Greek word for " sweet "— whilst it receives the latter from its occurrence in the Beryl.
Just as it was shown that the Ruby and the Sapphire are identical, save in colour, so the chemist has found that the Emerald, the Beryl, and the Aquamarine are practically the same mineral, the distinctions between the three varieties being due to differences of colour and other characteristics of only trivial value to the chemist, though of immense importance to the jeweller as affecting their commercial value.
That the true Emerald was known to, and held in estimation by, the Ancients, may be inferred from the fact that ornaments of Emeralds have been excavated from Pompeii and Herculaneum; that similar ornaments have
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