Page:Collier's New Encyclopedia v. 09.djvu/137

LEFT STONES, PRECIOUS 103 STONINGTON lapis lazuli, crocidolite, labradorite, moon- stone, avanturine, and malachite. To the list of precious stones there should be added two substances of animal origin — pearls and red coral — and perhaps also amber, a comparatively rare and valu- able fossil resin. When luster and sparkle are the prin- cipal qualities to be revealed, as in the case of the diamond, the surface is most favorably cut into numerous plane facets as either brilliant or rose cut stones. When color is the more important quality of the stone it may, if plane surfaces are wanted, be step or table cut. Such stones also, and translucent and opaque stones, may be cut en cabochon — i. e., with curved or rounded surfaces. Ore of the most important qualities of a precious stone is its hardness, as on that property depends its power of re- sisting wear and of keeping the bril- liance of its polished surface. It is a property of great constancy, moreover, and in many cases affords a ready means of determining the nature of a stone un- der examination. Of all known sub- stances diamond is the hardest, and rep- resenting it, according to Mohs's scale, by 10, the following is the relative hard- ness of several of the more important of the precious stones: diamond, 10.0; sap- phire, 9.0; ruby, 8.8; chrysoberyl, 8.5 spinel, 8.0; topaz, 8.0; aquamarine, 8.0 emerald, 7.8; zircon, 7.8; tourmaline, 7.5 amethyst, 7.0; moonstone, 6.3; turquoise, 6.0; opal, 6.0. The value of the precious stones produced in the United States in 1919 was $123,046. The largest in value was corundum, $40,304, followed by turquoise, $30,537; quartz, $19,078, and tourmaline, $18,642. See Diamond; Gem. Artificial Precioiis Stones. — Numerous attempts have been made by eminent in- vestigators to produce artificial precious stones by means of intense heat and pressure and by electrical action; but hitherto these efforts have failed of prac- tical success. In an important memoir published by Sainte Claire Deville and Caron in 1858, they describe various processes by which they obtained small crystals of corundum, ruby, sapphire, etc. By the action of the vapors of fluoride of aluminum and boracic acid on one an- other, they obtained crystals which, in hardness and in optical properties, re- sembled natural corundum. When a lit- tle fluoride of chromium was added a similar process yielded violet-red rubies; with rather more fluoride of chromium blue sapphires were yielded; and with still more green corundum was obtained. A mixture of equal equivalents of the fluorides of aluminum and glucinum, when similarly acted on by boracic acid, yielded minute crystals of chrysoberyl. The action of fluoride of silicon on zir- conia yields small crystals of zircon, and by the action of silica on a mixture of the fluorides of aluminum and glucinum hexagonal plates of extreme hardness were obtained, which in some respects resembled emerald. In subsequent researches Becquerel, by the use of electric currents of high tension succeeded in obtaining opals, etc., from solutions of silicates. Among the most successful of experimenters in this direction was Ch. Feil, of Paris, who successfully crystallized alumina, and by the introduction of coloring matter pro- duced sapphires and rubies identical in hardness and composition, but not in brilliance, with the natural stones. M. Feil also succeeded in preparing true crystals of spinel, and a blue lime spinel of great hardness, but which were glassy rather than crystalline in structure. Imitations of precious stones consist of a soft, heavy flint-glass called strass, or paste, appropriately colored, and they may readily be distinguished, among other peculiarities, by their great soft- ness. Fraudulent combinations are made by cementing thin plates of precious ma- terials over, and sometimes under, a body of valueless glass. STOISTEWALL JACKSON, a name given to Gen. T. J. Jackson during the Civil War. See Jackson, Thomas J. STONEWARE, a very hard kind of pottery, with which are made jars, drain pipes, and a variety of chemical utensils. It is constituted of plastic clay, united in various proportions with some felspathic minerel sands of different kinds, and in some cases with cement, stone, or chalk. These mixtures are then subjected to a heat sufficiently great to cause a partial fusion of the mass. This condition of semi-fusion is the distinguishing char- acter of stoneware. The finer varieties of stoneware are made from carefully selected clays, which when burnt will not have much color. These are united with some fluxing substance, by which the par- ticular state of semi-fusion above men- tioned, is brought about. Formerly the glaze of stoneware was always a salt glaze ; recently, however, it has been cus- tomary to glaze with a mixture of Cornish stone, flint, etc., as in the manu- facture of earthenware. See Pottery. STONINGTON, a town in New London CO., Conn.; on the Long Island Sound, and on the New York, New Haven, and Hartford railroad; 43 miles S. W. of Providence, R. I. It comprises the bor- ough of Stonington and the villages of