Page:The American Cyclopædia (1879) Volume VII.djvu/122

 114: FELANITX FELDSPAR 1810). One of his finest tragedies is Ines de Castro (1793), and his most finished prose writings are Brieven over verscheiden onderwer- pen (6 vols., 1784-'94). A complete edition of his works was published soon after his death (11 vols., Rotterdam, 1824). FELAMTX, or Felaniche, a town of Spain, on the island of Majorca, 25 m. E. S. E. of Palma; pop. about 8,000. It is in a fertile valley sur- rounded by mountains, and contains spacious streets and six squares. There is an ancient Moorish castle, with a subterranean vault, on the adjoining mountain of San Salvador de Felanitx. An active trade is carried on in cattle, wine, fruit, and colonial produce. Linen and woollen goods and other articles are manu- factured. The place is of great antiquity. The neighboring mountains abound with Moorish remains. FELDKIRCH, a town of Austria, in Vorarl- berg, on the 111, and on the railway leading from the Tyrol into Switzerland, 20 m. S. S. W. of Bregenz ; pop. 3,000. It is the seat of a vicar general who has jurisdiction over all the churches of Vorarlberg, and of a Jesuit college which has a large number of pupils from Aus- tria, Germany, and other countries. It has cotton mills, machine and fire engine facto- ries, a bell foundery, tile worksj manufactories of articles of wood, distilleries of Kirschwasser, and an extensive trade. FELDSPAR (Ger. Feldspath, from Feld, field, and Spath, spar), a species of aluminous mine- rals very abundantly distributed, principally in plutonic and volcanic rocks, as granite, gneiss, greenstone, and trachyte. The different spe- cies were formerly confounded, but they are now distinctly classified, not only by the differ- ent crystalline forms which they present, but, when these are the same, by distinct chemical composition. The feldspars are in all cases anhydrous double silicates, consisting of a sili- cate of alumina combined with a silicate of some one or more of the protoxides of potash, soda, lithia, baryta, or lime. The proportion between the aluminous or sesquioxide base and the protoxide bases is constant, being one equivalent of each, making the oxygen ratio 1 to 3; but the proportion of silica varies, causing considerable variation in the density and hardness. The amount of silica corre- sponds much to that in the rock in which the feldspar is found, and to the minerals asso- ciated with it, the more highly silicated kinds occurring in granite, and the less silicated in basalts. When a granite has large crystals of feldspar disseminated through it, it is called porphyritic granite, and sometimes porphyry, particularly when the proportion of feldspar is large. The various species of feldspar are given in the following table, as classified by Prof. Dana, with their systems of crystalliza- tion, and also their composition as indicated by the oxygen ratios of constituents ; the first col- umn of figures showing the protoxide, and the second the aluminous base, while the last col- umn gives the proportion of silica according to the same ratio : NAME OF FELDSPAR. System of Crystallization. Proportion of Constituents. Anorthite, lime feldspar Labradorite, lime-soda feldspar.. Hyalophane, baryta-soda " . Andesite, soda-lime " Oligoclase, " " " . Albite soda feldspar. Triclinic.... Monoclinic . Triclinic.. . . Monoclinic . 1 1 1 1 3 3 8 3

8 3 4 6 8 8 9 12 12 Orthoclase, potash feldspar All the feldspars may be fused before the blow- pipe, with more or less difficulty, to a vitreous enamel, and this property causes them to be extensively used for glazing porcelain. The crystals of the several varieties range in hard- ness from 6 to 7 upon a scale of 10, being harder than glass, but less so than quartz. Their specific gravity varies from 2 '5 in ortho- clase to 2'7 in labradorite. The crystals of some species exhibit a beautiful play of colors ; labradorite, the lime-soda feldspar, first dis- covered by the Moravian missionaries on the shores of St. Paul's isle off the coast of Labra- dor, being the most beautiful. The splendid opalescent and chatoyant reflections of this mineral have made it much prized as an article of jewelry. The cause of the play of colors has been satisfactorily explained by Reusch, who finds a cleavage structure of extreme del- icacy transverse to the median section. He therefore regards the color as that of thin plates, produced by the interference of the rays of light. The more common feldspars are orthoclase, or common potash feldspar, and albite, or soda feldspar. The potash species is the one most frequently met with, and is the usual associate of mica and quartz in ordinary granite, and of hornblende and quartz in sy- enitic granite. Fine crystals of orthoclase are found at Carlsbad and Elnbogen in Bohemia ; at St. Agnes in Cornwall; in the Mourne mountains in Ireland, associated with beryl and topaz ; in great abundance in trachyte at Drachenfels, on the Rhine; and also in the lavas of Vesuvius, in the valley called Fossa Grande. In the United States, it is found at Mt. Desert on the coast of Maine, of a fine green ; in Massachusetts, at South Royalton and Barre, in large crystals; in Connecticut, in the gneiss quarries at Haddam, and the feldspar quarries at Middletown, in crystals a foot long and from 6 to 8 in. thick ; in New York, at Potsdam, St. Lawrence co., in crystals a foot thick, at Warwick, Orange co., asso- ciated with tourmaline and zircon, and in many other places. The formula of orthoclase is K 2 O, A1 4 O 3, 6SiO a. The old formula, regard- ing silica as SiO 3 and using the small atomic weight of oxygen, is KOSiO s, Al 2 O 3 3SiO 8. Albite, or cleavelandite, the soda feldspar, often replaces orthoclase as a constituent of granite, and in some instances is associated with it, as in Pompey's pillar, when it gene- rally has a whiter color. Veins of albite