1911 Encyclopædia Britannica/Amethyst
|←Amesbury (Massachusetts)||1911 Encyclopædia Britannica, Volume 1
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AMETHYST, a violet or purple variety of quartz used as an ornamental stone. The name is generally said to be derived from the Gr. ἀ, “not,” and μεθύσκειν, “to intoxicate,” expressing the old belief that the stone protected its owner from strong drink. It was held that wine drunk out of a cup of amethyst would not intoxicate. According, however, to the Rev. C. W. King, the word may probably be a corruption of an Eastern name for the stone.
The colour of amethyst is usually attributed to the presence of manganese, but as it is capable of being much altered and even discharged by heat it has been referred by some authorities to an organic source. Ferric thiocyanate has been suggested, and sulphur is said to have been detected in the mineral. On exposure to heat, amethyst generally becomes yellow, and much of the cairngorm or yellow quartz of jewellery is said to be merely “burnt amethyst.” Veins of amethystine quartz are apt to lose their colour on the exposed outcrop.
Amethyst is composed of an irregular superposition of alternate lamellae of right-handed and left-handed quartz. (See Quartz.) It has been shown by Prof. J. W. Judd that this structure may be due to mechanical stresses. In consequence of this composite formation, amethyst is apt to break with a rippled fracture, or to show “thumb markings,” and the intersection of two sets of curved ripples may produce on the fractured surface a pattern something like that of “engine turning.” Some mineralogists, following Sir D. Brewster, apply the name of amethyst to all quartz which exhibits this structure, regardless of its colour.
The amethyst was used as a gem-stone by the ancient Egyptians, and was largely employed in antiquity for intaglios. Beads of amethyst are found in Anglo-Saxon graves in England. Amethyst is a very widely distributed mineral, but fine clear specimens fit for cutting as ornamental stones are confined to comparatively few localities. Such crystals occur either in cavities in mineral-veins and in granitic rocks, or as a lining in agate geodes. A huge geode, or “amethyst-grotto,” from near Santa Cruz in southern Brazil, was exhibited at the Düsseldorf Exhibition of 1902. Many of the hollow agates of Brazil and Uruguay contain a crop of amethyst-crystals in the interior. Much fine amethyst comes from Russia, especially from near Mursinka in the Ekaterinburg district, where it occurs in drusy cavities in granitic rocks. Many localities in India yield amethyst; and it is found also in Ceylon, chiefly as pebbles.
Purple corundum, or sapphire of amethystine tint, is called Oriental amethyst, but this expression is often applied by jewellers to fine examples of the ordinary amethystine quartz, even when not derived from Eastern sources.
Amethyst occurs at many localities in the United States, but rarely fine enough for use in jewellery. Among these may be mentioned Amethyst Mountain, Texas; Yellowstone National Park; Delaware Co., Pennsylvania; Haywood Co., North Carolina; Deer Hill, and Stow, Maine. It is found also in the Lake Superior district.
See G. F. Kunz, Gems &c. of North America (1890), and Report for 12th Census (vol. “Mines and Quarries”). (F. W. R.*)