from gneisses, granites, trachyte, basalt, sanidine bombs, and graywackes, and has described the characteristic peculiarities of crystals obtained from these different sources. He has found that the crystals occurring in gneisses always present rounded contours, while those in granite are always defined by sharp crystal planes. He proposes to make use of this fact in distinguishing gneisses with granitic habit from true granites. Mineralogical News.-Kaliophilite is the name proposed by Mierish' for a new mineral occurring in colorless needles in one of the Monte Somma bombs examined by him in the course of his work referred to in the March number of this journal. It is a potassium nepheline. An analysis yielded,— 8 Na,O The author supposes that ordinary nepheline may consist of mixtures of the isomorphous molecules K,Al,Si2O and Na,Al¿Si2O8, since this mineral always contains more or less potassium. The group of nephelines is now known to consist of at least three members, the third being the mineral eucryptite, discovered by Brush and Dana among the alteration products of spodumene. -Scapolite.-In no manner can the difference in the views of the two schools of mineralogical chemists be better learned than by an examination of the papers relating to the discussion now being carried on in Germany and Austria in regard to the nature of the scapolite group of minerals. In an article in the Neues Jahrbuch, Rammelsberg3 gives his reason for considering this group of minerals as consisting of molecular combinations of normal- (meta-), half- (ortho-), and di- (bi-) silicates of sodium, calcium, and aluminium in certain definite proportions. Sarkolite, for instance, he regards as a molecular compound made up of the three ortho-molecules in the proportions 3Na,SiO4, 27Ča,SiO4, 10Al(SIO),; and Meionite, from Mt. Vesuvius, as a similar compound, in which the meta-silicates are present in the proportions of one molecule to six of the ortho-silicates, as, Na SiO 6 { 4Ca2SO Tschermak, on the other hand, regards the members of this group (like those of the plagioclase group) as isomorphous mixtures of the two molecules 4CaO,3Al2O3.6SiO2 = Ca, Al,SiO25 and Na.AlSi18O48 Cl2 3Na,O,3Al2O3,18ŠiO2 + 2NaCl, which he calls respectively the meionite and mariolite molecules. By Tschermak's Min. u. Petrog., Mitth. viii., 1886, p. 156. 2 Amer. Jour. Sci., III. xx., 1880, p. 257. 3 Neues Jahrbuch f. Min., etc., Beil. Band, iv., 1886, p. 610; also Sitzb. Berl. Akad., Bd. 30, p. 589. 4 Min. u. Petrog. Mitth., vii., 1886, p. 400. the combination of these two molecules in different proportions the various members of the group are formed, and by calculation the proportionate amounts of each present in any given case can readily be determined from the amounts of calcium and sodium found by analysis.-Bastonite, a micaceous mineral characterizing certain sandstones and arkoses, is supposed by Renard to be very similar to vermiculite, which Tschermak regards as an altered phlogopite. Its analysis yielded Klement,'— SiO2 Al2O3 Fe2O, FeO MnO CaO MgO KO Na2O HO -According to the investigations of Nordenskiöld,2 the peculiar fluid inclusions in Brazilian topaz, to which Dana gave the name "brewsterlinite," are, at least in some cases, inclusions of a hydrocarbon, probably of the naphtha group. Schuster3 has discovered that the braunite from the manganese mines of Jakobsberg, in Wermland, Sweden, is probably isomorphous in crystallization with hematite and ilmenite. Its analysis yielded Igelström, Sio, MnO 80.23 FeO MgO.CaO РЬО 8.65 8.17 8.7 If the iron, magnesium, calcium, and lead be supposed to replace manganese, the composition of the mineral may be represented by the formula 11MnO3.3MnSiO3, corresponding very nearly to the result reached by Rammelsberg in his analysis of the braunite from Elgersburg. Crystallographic News.-Recent measurements of crystals of vanadinite from Pinal County, Arizona, have yielded Mr. Penfield 5 results agreeing closely with those obtained by Urba in his investigations of Carinthian crystals. Endlichite [Pb,Cl (AsO4)3 + Pb,Cl(VO)] from the Sierra Grand Mine, Grant County, New Mexico, was also examined. The axial ratio, as determined by Penfield, is a:c=1:-7495. The presence of arsenic in the mineral seems to tend to increase very perceptibly the length of the vertical axis as compared with that of the pure vanadium mineral (in vanadinite a:c=1:.7112).—The new forms 20, 1106, and 604 have been observed by E. S. Dana on crystals of native copper. In the same paper the author describes crystals which, by development in certain directions, assume the rhombohedral symmetry. The twinning laws of copper are also investigated, and the article concludes with plates containing fiftyMin. u. Petrog. Mitth., viii., 1886, p. 1. 2 Neues Jahrb. f. Min., etc., 1886, i. p. 242. 4 Annales des Mines de Wermland, 1884, p. 73. 5 Amer. Jour. Sci., December, 1886, p. 441. 6 Zeitschrift f. Kryst., iv. p. 353 7 American Naturalist, Notes, July, 1885, p. 709. 8 Amer. Jour. Sci., December, 1886, p. 413. 8 four illustrations of copper crystals and crystal groupings. From new measurements of crystals of hyalosiderite, the iron-rich olivine, and forsterite, the pure magnesian variety, Max Bauer1 has recalculated the axial relations of these minerals. For the first he finds a:b:c=.46815:1:.58996; for the second, a:b:c= .46476: 1.58569. On comparing these ratios with those obtained from measurements made on fayalite, the pure iron olivine, and other members of this series, the composition of which is known, it is found that an increase in the amount of the magnesium molecule present in any case is accompanied by a shortening of the a and c axes as compared with the b axis.In the same article Bauer describes twinning lamellæ in massive barite from several localities in Germany. The twinning plane is 6P. He regards them as pressure twins like those found in calcite, cyanite, sphene, etc. Miscellaneous. In the January number of the American Fournal of Science Mr. G. F. Becker has an interesting article on “The Texture of Massive Rocks." The subject is treated theoretically, and in such a manner that a brief synopsis of it would be most unsatisfactory. Suffice it to state here that Mr. Becker supposes the formation of plutonic granitoid rocks to represent an extreme and highly exceptional case of neutral chemical equilibrium in a pasty magma, by the cooling of which they were derived. As a rule, however, he regards granular structure as characteristic of metamorphosed sediments.3 Porphyrite structure is the natural result of slow cooling of a very fluid magma, and is merely the evidence of fractional crystallization. of the various minerals. These conclusions are based on a theory of the solidification of minerals in accordance with certain. laws of thermo-chemistry.In a letter to the Neues Jahrbuch für Mineralogie,5 A. Schrauf explains his views on morphotropism and atometrie, which, so far as they relate to minerals, are briefly as follows. The form of crystallization of chemical mixtures depends principally upon the various amounts of their constituents. MgSO+7H2O (epsomite) crystallizes in the orthorhombic system, while FeSO, +7H2O (melanterite) is monoclinic. Mixtures of MgSO,+7H2O and FeSO, + 7H2O crystallize in the latter system until the proportion of magnesium in the mixture is to the amount of iron as three atoms to one atom (3MgSo, + FeSo1) + 7H„O, when it crystallizes in the orthorhombic system,-i.e., the crystallization is determined by that substance which is in excess (by weight). In the compound (3 MgSo̟, + FeSo、) + 7H2O the Mg and Neues Jahrb. f. Min., 1887, i. p. I. 2 Amer. Jour. Sci., January, 1887, p. 50. 3 Cf. American Naturalist, Notes, December, 1886, p. 1050. 5 Neues Jahrb. f. Min., 1886, i. p. 234. Fe are to each other as 72: 56, Mg is in excess, and the substance crystallizes as does MgSo,+7H2O. In compounds containing less Mg (as 2MgSo, + FeSo,)+7H2O, the proportions of Mg and Fe are as 48: 56, and the crystallization is that of melanterite. Various conditions effect the crystallization of mixed bodies, but the most important of these, according to Schrauf's opinion, is the one mentioned above. If this law is found to be general in its application, the present views in regard to the dimorphism of many compounds belonging to the so-called iso-dimorphous groups will have to be modified. May 9, 1887. |