MINERALOGY AND PETROGRAPHY.' Petrographical News.-A contribution to the knowledge of the geology of South America has recently been made by Bergt2 through the study of thin sections of rocks collected in the Sierra Nevada and the Sierra de Peryȧ in the United States of Columbia. Bergt has confined himself to a description of a large number of rocks that were collected by others, and therefore he has not been able to do more than indicate the interesting results which follow from a close study of their thin sections. Among the facts of general interest discovered may be mentioned the formation of secondary epidote from augite and olivine in melaphyre, and the production of an epidosite therefrom; the occurrence of lamellæ in uralite of syenite, that have became curved through the pressure exerted upon them by a feldspar crystal during its growth; the existence of a rim of brown hornblende around a grain of uralite, and the occurrence of secondary brown mica as a product of the alteration of augite. The writer also discusses the nature of uralite, and suggests that the name uralitite be used as a comprehensive one for those rocks containing secondary hornblende, whose original nature cannot be determined.-Goller 3 describes in a very careful article a number of lamprophyre dykes cutting gneiss and crystalline schists in the Vorspessart in Germany. The crystalline schists consist of dioritic and "augen " gneisses, produced by pressure from eruptive rocks, and other gneisses, the history of whose origin is unknown. They are cut by dykes of camptonite and kersantite, whose characteristics are minutely described by the author. Both contain large quartz and orthoclase grains that are supposed to be the remnants of dissolved inclusions, and smaller quartzes that have crystallized from the magma. Two varieties of augite were observed; one alters into talc and tremolite through green hornblende, and the other into serpentine through the same intermediate product. The original quartz is supposed to owe its origin to the physical conditions. prevailing during the solidification of the rock mass-principally pressure and the presence of water. Still other instances of the occurrence of young rocks with the characteristics of old ones are described by Reiser' from four localities in the northern Alps. They are typical diabases and diabase porphyrites of Eocene age. They con 1 Edited by Dr. W. S. Bayley, Colby University, Waterville, Me. 2 Min. u. Petrog Mitth., 1889, X., p. 271. Neues. Jahrb. f. Min., etc., B. B. VI., p. 485. Min. u. Petrog. Mitth., X., 1889 p. 500. sist of plagioclase, augite, apatite and secondary substances, and occur with the typical structure of granular and aphanitic diabases. They are characterized by the zeolitization of the plagioclase. Among the zeolites formed are natrolite and analcite, of which the latter has been separated and identified by chemical means. -Thin veins of diabase with tachylite borders have produced fusion along the edges of the slates through which they cut. According to Rutleys the glassy rim produced by the fusion is darker in color than the tachylite selvages of the dyke rock.————-N. H. and H. V. Winchell propose a new theory for the origin of the iron ores of Minnesota, in opposition to the iron carbonate theory of Irving. The new theory follows the same lines as does Hunt's crenitic hypothesis. It is based entirely on theoretical suppositions, which, so far as is known, can have little foundation in facts. 8 Mineralogical News.-Rare Minerals.-In an article on the minerals of Fiskernäs, in Greenland, Ussing has given the crystallographic and optical properties of several rare minerals. Sapphirine has for its axial ratio a: b: c.65: 1; .93. B=79° 30′. The axis of least elasticity is inclined 8° 30' to the vertical axis, and 2Vna = 68° 49′. The indices of refraction are a = 1.7055, B=1.7088, r = 1.7112. The mineral is negative, and is pleochroic with A colorless, and B and C = blue, or A = light greenish blue, B = dark bluish green, and C=yellowish sap green. An analysis of the mineral yielded : MgO Loss .31 Sio, Al,O, Fe2O, FeO Kornerupine is orthorhombic with a: b = .854: 1. It has a specific gravity of 3.273, is colorless in thin section, and has ∞ Po as the plane of its optical axes, with the acute bisectrix, which is negative. The optical properties of gedrite and pargasite are also investigated. In a few general remarks on the properties of the former mineral the author states that it is more probable that the optical angle of the orthorhombic hornblendes increases with the increase in the percentage of silica rather than with the increase of iron.- -Atelesite, analyzed The axial ratio, recalculated from von Rath's measurement, is a : b: c= .9297: 1: 1.5123. B=69° 35′. New measurements by Busz gave a: b: c = .9334: 1: 1.5051. B=70° 43′.—Kobellite, from the Silver Bell Mine, Ouray, Colorado, has been analyzed by Kellar.10 Its composition is: Gangue S Bi Sb Pb Ag Cu Fe Zn which may be represented by 2(Pb.Ag,Cu,) S. (BiSb),S,. It differs .58 It It is allied to bröggerite (3RO. UO,) and clevéite (6RO.2UO,.3H,O) in containing a large proportion of uranium. Its hardness is 5.5, and its composition is represented by (9RO.4UO,.3H,O). Two varieties of fergusonite have been found in the same locality. The first corresponds to Cb2O.RO,.H,O, and the second to Cb2O.RO,. 3H,O. The two are closely associated. The first is probably tetragonal, with a bronzy lustre on a fresh fracture. It is infusible, decrepitates when heated, and changes to an olive green color. The second variety is deep brown in color. Its streak is greenish gray. Upon ignition it turns light brown but does not decrepitate.Hydrocerussite (2PbO, + Pb(OH), corresponding to azurite among the copper salts, has been produced by Bourgeois, 13 by acting upon lead acetate with ammonium carbonate. The little crystals thus formed have all the properties of the natural substance. By means of them the composition of the mineral has been determined. The white lead of commerce is found by the author to be a mixture of two substances with the composition respectively of cerussite and hydrocerussite. Percylite and caracolite are briefly mentioned by Fletcher 1a 10 Zeits. f. Kryst., 1889, XVII., p. 67. 11 Jour. Amer. Chem. Soc., Vol. VII., No. 7. 12 Amer. Jour. Sci., Dec. 1889, p. 474. 13 Bull. Soc. Franc. d. Min., XI., p. 221. 14 Min. Magazine, 1889, p. 171. |