(EXTRACTED FROM THE AMERICAN NATURALIST, August, 1887.) MINERALOGY AND PETROGRAPHY.2 Petrographical News.-Very recently Professor Judd3 has undertaken to show that his schillerization theory is founded upon well-known facts. In addition to the planes of least cohesion (cleavage planes) and the gliding planes, there is a third series of planes in crystals, the solution planes, along which the solution of the crystal takes place most readily. These are distinct from both the cleavage and the gliding planes, and their position in the crystal is dependent upon its symmetry. When a crystal fragment is subjected to the action of a solvent, solution begins along these planes, little irregular-shaped hollows appear, and as these grow larger they assume the form of negative crystals. These hollows gradually become filled with secondary substances, and in this way arise the inclusions, which 2 Edited by Dr. W. S. BAYLEY, Madison, Wisconsin. 3 American Naturalist, Dec. 1885, p. 1216. 4 Geological Magazine, vii., Dec. 1886, p. 81. produce the peculiar shimmer on faces of the crystal parallel to the planes along which the inclusions are arranged,-i.e., the solution planes. After showing that secondary solution planes may be produced in directions parallel to directions of pressure, as in the case of a faulted quartzite pebble, and that the repeated twinning of a mineral may also give rise to them, the author describes various stages in the process of schillerization, as seen in thin sections under the microscope. This theory is not intended to apply to all cases of inclusions arranged in definite planes in minerals, but only to those which at the same time show some indication of regularity of form, as in labradorite, hypersthene, etc.- -On the road between Verrex and St. Vincent, in the Val d'Aoste, Professor Bonney' has found a schistose glaucophane-eclogite interbedded with quartz-mica schists, limestone, and green schists. The rock consists of pale winered garnets, with inclusions of hornblende, glaucophane, and dust, a green hornblende, glaucophane both in irregular grains and in well-developed crystals, epidote, mica, and sphene (leucoxene). In this connection the author describes in some detail the glaucophane-gabbro of Pegli, near Genoa. This rock was described by Williams as an amphibolite, but Bonney prefers calling it gabbro. The glaucophane appears to have been secondarily derived from diallage. Specimens of kaolinized granite from St. Austell, Cornwall, indicate to F. H. Butler the close association of tourmaline with the progress of the alteration in the original granite. According to Professor Bonney,3 the Rauenthal serpentine is not the result of the alteration of amphibolite, as was supposed by Weigand, but has been derived. from an olivine-hornblende rock resembling certain picrites. To this view Mr. Teall takes exception. He states that his examination of the rock confirms the deductions of Weigand, and that the serpentine is the product of the alteration of hornblende. The elastic sandstone of Delhi, Germany, according to O. Mügge, is composed of quartz grains intricately interlocking, and a very little interstitial clayey material. Most of the cement has been removed by the action of percolating waters, and in the interstices thus left the individual quartz grains have grown by the addition of silica in crystallographic continuity with the substance of the original grains. This growth, however, ceased before the occupancy of the entire space. It is to the abundance of these cells that the sandstone owes its elasticity.-Gonnard mentions the occurrence of phillipsite, chabasite, and apophyllite in the vacuoles of the basalt Geological Magazine, vii., July, 1886, p. 1. I Neues Jahrb. f. Min., 1882, ii. p. 201. 3 Geol. Magazine, Feb. 1887, p. 65. of Prudelles, Puy-de-Dôme.A mica-gneiss similar to the granulite of Törnebohm is described by Sjögren2 as occurring in the iron regions of the Banat. Sjögren finds that the ores are not connected genetically with the intrusion of banatite, as has heretofore been supposed.In his geological sketch of part of the Galician-Hungarian East Carpathians Dr. H. Zapalowicz3 gives a few notes on the schists and intrusive rocks occurring in the more mountainous regions of the Carpathians. Mineralogical News.-Stüvenite is the name proposed by Darapsky for a mineral from the Alcaparroso Mine, near Copiapó, in Chili. Its analysis yielded: This corresponds to a composition represented by the formula (Na, Mg)SO, + A12(SO4)3 + 24H,O. The mineral occurs in acicular crystals grouped in radial masses. Before the blowpipe it presents the features of the alums, to which group of minerals the new substance probably belongs.—In the same paper in which stüvenite is described Darapsky records the results of the analyses of a large number of Chilian alums, principally of the feathery variety, and gives a list of all the alums. investigated up to the present time. These he divides (following Dana) into the regular alums and the halotrichites, to which subdivision the above-noted stüvenite belongs. The names of seventeen distinct minerals are included in the list.――Hintze 5 proposes arsenolamprite as the name for Chilian arsenic, which possesses physical properties different from those of ordinary arsenic. The composition of the mineral is: As 98.20 Fe 0.96 Sio, (Mean of two analyses). Specific gravity is 5.50. It is soft, and of a brilliant metallic lustre. It is probably identical with the arsenglanz of Breithaupt, from Marienberg, in Saxony. In 1881, Luedecke attempted to show that mesolite, natrolite, and scolecite form an isomorphous-trimorphous group, the first mineral crystallizing in the orthorhombic, monoclinic, and triclinic systems, natrolite in the orthorhombic and monoclinic, and scolecite in the monoclinic and triclinic systems. C. Schmidt recently having the opportunity to reinvestigate the crystallography of scolecite, ' declares that this mineral crystallizes only in the monoclinic system, and that the triclinic variety described by Luedecke was I probably merely a monoclinic twin, whose twinning plane is the clinopinacoid. Since Rammelsberg has shown that the orthorhombic mesolite (galactite) is probably natrolite, and since this mineral is found only in orthorhombic crystals, there has as yet been no proof given to show that either of the three minerals mentioned crystallizes in more than one system.-A. Becker2 has analyzed alstonite and barytocalcite from Alston Moor, in order to decide as to whether Groth's view in regard to the composition of these substances is well founded. Both minerals are carbonates of calcium and barium, alstonite crystallizing in the orthorhombic system, and barytocalcite in the monoclinic. From the fact that calcium carbonate has never been found in monoclinic crystals, whereas, on the other hand, an orthorhombic variety is well known, Groth supposed that alstonite is an isomorphous mixture of the carbonates of barium and calcium, while barytocalcite is a molecular compound of the formula BaCa(Co)2. Becker's results indicate the truth of this supposition. The composition of alstonite may be represented by BaCa(CO3)2; that of barytocalcite by X BaCo, + YCаCo,. In the ruins of old mines in the neighborhood of the Windgälle, in Canton Uri, Switzerland, are found oolitic masses composed of a brown or green substance in little elliptical and lenticular grains cemented together by carbonate of lime. These little grains are themselves made up of scaly magnetite and a bright-green, weakly-dichroic mineral,3 with aggregate polarization. This was separated by Thoulet's solution, freed as perfectly as possible from the associated carbonate, and subjected to analysis, with the following result: Upon comparison of these figures with those found by Boricky for the chamoisite from Chrustenic, in Bohemia, the two minerals were found to be almost identical in composition, after allowing for the impurities in the Chrustenic mineral. Chamoisite is thus shown to be the alumina-rich and ferric-iron-free member of the series to which cronstedtite and thuringite belong.—The ferric sulphate botryogen, from Fahlun, in Sweden, has been examined by Hockauf. The mean of two analyses yielded : So Fe2O3 FeO 36.94 16.38 2.23 MnO CaO MgO H&O 33.99, corresponding to the formula FeSo1 + [Fe2(S0)3 + (FeO)¿So1]. The botryogen of commerce was also analyzed, and found not to have the composition of the genuine mineral. I Mineralchemie, ii., Aufl. 2, p. 633. 2 Zeits. f. Kryst., xii. p. 222. 4 Zeits. f. Kryst., xii. p. 240. = Crystallographic News.-R. Sharizer has studied the physical properties of monazite from a pegmatitic granite-vein near Schültenhofen, in the Böhmerwald. He finds it to crystallize in the monoclinic system, with an axial ratio 0.9735: 1:0.9254. The inclination of the à to the axis is 103° 37'. The plane of the optical axes is perpendicular to the clinopinacoid, and the acute bisectrix, which is positive, is in the obtuse angle ß, and is inclined 5° 54′ to the vertical axis. The optical angle VV 12° 44' for yellow light, and the indices of refraction ẞ = 1.9465 and 7 1.9285.In an article on hemimorphic pyrargyrite twins from Andreasberg, Schuster discusses the classification of twinned crystals, and defines them as symmetrical or unsymmetrical. The symmetrical ones he subdivides into those. hemitropically developed and those which show no hemitropism. The hemitropic symmetrical twins include those of holohedral and of certain hemihedral and hemimorphic minerals. The unsymmetrical and the non-hemitropic symmetrical classes embrace the twins of those minerals which crystallize in the inclined and trapezohedral-hemihedral divisions of the different systems, and also certain hemimorphic minerals. Examples are cited to show the application of the terms of this classification to the description of complicated twins.As the result of new investigations with the Bertrand 3 microscope and lenses, Des Cloizeaux finds that the mineral which bears his name crystallizes in the orthorhombic system.-Cathrein 5 describes crystals of orthoclase in the pores of granite at Predazzo, which have their largest development in the direction of their à axis.—The same author mentions twinning striations parallel to the octahedral edges of magnetite from Fürtschlagl, in the Zillerthal. Miscellaneous.-J. Lehmann' explains the perthitic structure of certain of the feldspars by supposing that one of the minerals, as albite in perthite, is secondary, and fills cracks in the other. The cracks he further supposes to be occasioned by contraction in the original mineral, in consequence of sudden cooling, etc. He shows, by experimenting on a large number of different minerals, that this cracking takes place, under certain conditions, not in the direction of the cleavage, but in some other direction,usually at right angles to the most perfect of all the cleavages. In the case of orthoclase, in which the cleavages are parallel to ∞P and OP, the cracking takes place parallel to P∞. After formation in this manner the cracks are enlarged by the action of solvents and the secondary substance is deposited in them. The indices of refraction for topaz from the Urals, anglesite from Monte Poni, in Italy, sphalerite from Spain, and harstigite Zeits. f. Kryst., xii. p. 253. 3 Bull. d. 1. Soc. Min. de France, 4 Zeits. f. Kryst., xii. p. 178. 2 Ib., p. 117. 6 Ib., 608. |