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CHAPTER XVI.
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Definitions, Imports, and Production, Values, Cutting of Diamonds and Other Stones,
Watch Jewels, Collections of Gems, Minerals, and Jade, Uses of Precious
and Ornamental Stones for the Ornamentation of Silver,
and Furniture and for Interior Decoration,
Trilobite Ornaments.
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HAT is a precious stone? The answer to this question is not easy, for the value of a particular kind of stone is often due in great measure
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to the caprice of fashion, or to some adventitious circumstance of time or place; and some stones that are today of small value have, during certain periods in the past, almost displaced the diamond or the ruby in public estimation. Beauty of color, hardness, and rarity are the essential qualities which entitle a mineral to be called precious. Strictly speaking, the only precious stones are the diamond, ruby, sapphire, and emerald, though the term is often extended to the opal, notwithstanding its lack of hardness, and to the pearl, which is not a mineral but strictly an animal product.
Popularly, a gem is a precious or semi-precious stone, especially when cut or polished for ornamental purposes. Mineralogi-cally, the term designates a class or family of minerals hard enough to scratch quartz, without metallic lustre, but generally brilliant and beautiful, and includes the semi-precious or fancy stones (called pierres de fantaisie by the French), such as the chrysoberyls, alexandrites, tourmalines, spinel, and topaz. Ar-chaeologically, the term is restricted to engraved stones, such as
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