Phosphoric Acid in Chili Saltpetre. By C. OCHSENIUS (Jahrb. f. Min., 1887, 1, Mem., 221-222). The principal argument always brought forward against the theory of the formation of Chili saltpetre from guano, was that no phosphoric acid could be detected in the nitrate. The ordinary analytical methods give only negative results. The author has carefully examined a series of strata from the nitrate beds of Taltal, in the Chilian province of Atacama. He employed Streng's microchemical method, and obtained the unmistakable green rhombic dodecahedra of molybdenum-ammonium phosphate in the specimens from the beds above the nitrate deposit, and in the ordinary sodium saltpetre. No phosphoric acid could, however, be detected in the white, crystalline nitrate, or in the beds below the deposit. B. H. B. Some Chilian Alums. By L. DARAPSKY (Jahrb. f. Min., 1887, 1, Mem., 125-137).—1. Stüvenite.—An alum found in some abandoned workings at the Alcaparrossa Mine, near Copiapó, gave on analysis. the following results : H2O. SO 3. 36.1 Al03. MgO. Na2O. K2O. Total. 99.0 The formula is Na2O,SO, + MgO,SO3 + 2(Al2O3,3SO3) + 48H2O. For this well-characterised species the author proposes the name of stüvenite, in honour of Enrique Stüven. 2. Sesqui-magnesia alum.-Pure aluminium sulphate occurs frequently in Peru (see Field, this Journal, 1869, 259). A specimen from Cerros Pintados, in the National Museum of Santiago, only partially agrees with the descriptions hitherto published. In places, the mineral was considerably altered on the surface. When broken, however, it exhibited the remarkable fibrous character that occurs so frequently in all halotrichites. At one end of the specimen, the fibres pass into a pale pink crystalline mass. Analysis gave the following results:— I. Massive alum. II. Fibrous alum. III. Weathered powder. The formula of the massive alum is 2MgO,SO, + Al2O3,3SO3 + 28H2O, or that of picroalumogene. The formula of the fibrous alum, 3MgO,SO, + 2A120,3SO, + 53H2O, represents a sesqui-magnesia alum. B. H. B. Cristobalite from Mexico. By G. voм RATH (Jahrb. f. Min., 1887, 1, Mem., 198-199).-Near the summit of the Cerro S. Cristóbal, near Pachuca, in Mexico, the author found some white, regular crystals associated with tridymite. Their hardness was 6-7, and their sp. gr. 2-27. Analysis of a minute quantity gave the following results: These regular crystals consist essentially of silica. The question then arises, are the crystals pseudomorphs, or do they represent a new octahedral form of silica ? This can only be solved by collecting further material. Should it be desirable to give a name to this mineral, the author suggests that of cristobalite, from the locality where it was found. B. H. B. Artificial Production of Quartz and Tridymite. By K. DE CHROUSTCHOFF (Jahrb. f. Min., 1887, 1, Mem., 205–208).—In 1870, the author artificially formed for the first time the two crystallised modifications of silica. The crystals were, however, quite microscopic in character. He has recently succeeded in forming quartz in the wet way, and tridymite in the dry way. The products obtained are of remarkable beauty, finely developed columns of quartz with the two rhombohedra, and almost pure tridymite, the size of a bean. For the artificial production of quartz the author employed an aqueous solution of silicic acid (dialysed silica). Several quarter litre glass bulbs, 0.5 cm. thick, were half filled with a 10 per cent. aqueous solution of silica, and heated at 250° in an air-bath for several months. During the first day the silica separated out. In six months' time hard sandy grains were found in the white precipitate. These were collected and washed, and were found to consist of transparent, colourless, homogeneous, well-developed crystals of quartz, 05 mm. in size. In preparing tridymite artificially, the natural process was imitated, that is, by means of molten magmas artificial frittings were effected. Two series of experiments were conducted:-1. Rocks rich in quartz were melted with basalts or melaphyres, and kept in the molten state for 1 to 8 hours. 2. Rocks rich in quartz were fritted or quite melted alone in a charcoal coke fire. Both series of experiments yielded excellent specimens of tridymite. B. H. B. Artificial Production of Crystallised Silica and Orthoclase. By K. DE CHROUSTCHOFF (Compt. rend., 104, 602-603).-In part a description of the results given in the preceding Abstract. One of the quartz crystals showed several very small cavities with movable globules. In other experiments the solution of dialysed silica was mixed with a small quantity of dialysed alumina and of potassium hydroxide, the mixture being heated in flasks at 300° for several months. Under these conditions crystals of quartz similar to those formed in the first experiments were obtained, mixed with a small quantity of thin rhombic lamella, with the same properties as the adularian orthoclase obtained by Friedel and Sarasin. C. H. B. Composition of Felspars in the Island of Elba. By A. FUNARO (Gazzetta, 16, 523-526).—It is generally held by geologists that the quartziferous porphyry of Elba is a structural variety of the granite in that island, the difference being dependent on variations in consolidations of the original magma. This view is sup ported by the following analyses, which indicate no marked difference in the chemical composition of these two species of rock. I. Granite. II. Gneissic schist. III. Quartziferous porphyry: With the analysis of the granite that of the gneissic schist is also compared, from which it appears that the composition of these rocks is very similar; the greatest difference is evident in the proportion of the silica. This result offers some confirmation of the view of geologists that granite is formed from gneiss and other more or less felspathic schists. Probably boron was present in minute quantities in the three species of rocks above described. V. H. V. The Scapolite Series. By G. TSCHERMAK (Jahrb. f. Min., 1887, 1, Ref., 232-234).-The author submits the arguments brought forward by Rammelsberg (Abstr., 1886, 30 and 318) to severe criticism, and adheres to his theory that the members of the scapolite group are admixtures in different proportions of the two species meionite and marialite. The differences between the results of actual analyses of scapolite minerals and the theoretical results found by calculation, are quite insignificant. In conclusion, the author gives the following table, showing the calculated percentage compositions of the scapolite mixtures: By P. HAUTEFEUILLE and L. P. DE SAINT-GILLES (Compt. rend., 104, 508-510).-A mixture of 5 parts of the constituents of a highly ferruginous mica with 1 part of potassium silicofluoride melts between 1000° and a bright red heat, and loses fluorine somewhat rapidly in the form of silicon fluoride. If the mixture is allowed to crystallise whilst the proportion of fluorine remaining is still considerable, the solidified mass is more or less vesicular, but if the temperature is regulated so that crystallisation takes place when about 3 or 4 per cent. of fluorine is present, the product crystallises in the same form as mica, and has a similar composition. It forms thin pseudohexagonal plates, which are striated and macled, show polychroism, and melt before the blowpipe with intumescence. The crystals resemble the ferruginous mica of eruptive rocks, but have a slighter lower specific gravity, and are somewhat harder, but less elastic. These properties are well shown by magnetic crystals, which resemble the ferruginous micas of Vesuvius, and have the composition 6RO,2R203,9SiO2. By reducing the proportion of magnesia, crystals are obtained of the composition 4RO,2R20,9 SiO2, which closely approaches that of chromium mica. These crystals are harder and less elastic than those of mica. In some cases the increased hardness and diminished elasticity are due to admixture with a hard vitreous substance. The formation of crystallised minerals is facilitated by adding 10 per cent. of potassium arsenate to the fluorine-containing mixtures. If the silicate is allowed to solidify in an atmosphere of hydrogen, the product retains very little arsenic. The action of this gas produces intumescence, which facilitates the formation of geodes, and the latter contain crystals as much as 2 or 3 mm. in length. C. H. B. Talc, Pseudomorphite, and Muscovite from South Africa. By E. COHEN (Jahrb. f. Min., 1887, 1, Mem., 119-124).-The substances carved by the natives of South Africa are not only interesting ethnographically, but also mineralogically. They are found on investigation to be massive varieties of talc, chlorite, and muscovite. The talc is of a light grey colour with yellowish-brown streaks. Its sp. gr. is 2.794. Analysis gave— SiO2. Al2O3. FeO. FeO. MgO. H2O. Total. 27.13 4:40 100.90 The pseudophite was obtained from the Zoutpans Mountains in the Northern Transvaal. It closely resembles williamsite (serpentine). Its hardness, however, is less (2-3), and it fuses more easily. Analysis gave the following results : SiO2. Al2O3. Fe2O3. FeO. MgO. H2O. Total. 100-15 Of the water, 0.06 per cent. was given off between 100° and 300°, the remainder on ignition. The sp. gr. is 2:647. The hardness of all the varieties of massive muscovite examined is from 2 to 3. Analyses are given of a green variety with green and brown streaks (I), a yellow variety with yellow-ochre streaks (11), and a red variety, with brown and violet streaks (III):— Kersantite from Wüstewaltersdorf, in Silesia. By E. DATHE (Jahrb. f. Min., 1887, 1, Ref., 272-273).-The author has discovered a vein of kersantite in the culm beds at Wüstewaltersdorf, in Lower Silesia. The vein is 500 metres long and 80 to 100 metres broad. The principal constituents of the rock are plagioclase and magnesiamica, with augite, hornblende, and quartz; whilst apatite, magnetite, and calcite occur as accessory or secondary minerals. An analysis of the rock gave the following results : : SiO2. TiO2. Al2O3. FeO3. FeO. MgO. CaO. 56.18 0.45 15.51 2.86 3.94 5.46 3.69 Andalusite from Marabastad, Transvaal. By J. Götz (Jahrb. f. Min., 1887, 1, Mem., 211–212).—It has been stated that the andalusite in the ottrelite and andalusite schists of the Marabastad goldfields in the Transvaal, might be disthene. The author has consequently made a fresh investigation of the mineral in question. The sp. gr. he finds to be 3.11; that of distene is considerably greater. Analysis gave the following results:- The mineral cannot be disthene, on account of its specific gravity and the absence of perfect cleavage. B. H. B. New Analyses of Norwegian Rocks. By P. JANNASCH (Ber., 20, 167—176).—In 1855, T. Kjerulf published a number of analyses of the interesting rocks occurring in the vicinity of Christiania. The gaps in his series are now filled by new analyses, by the author, of rocks from the same district. The rock of most frequent occurrence has received various names, such as Christiania syenite, Drammen granite, and syenite porphyry. In all its modifications the soda felspar is in excess of the potassium felspar. It thus differs from the granites and syenites of the same age, and belongs to the group of rocks termed prædacite by Lang. It differs from the diorites and diabases in the constant proportion of primary quartz. The mineral constitution of the rock is very variable, the prevailing constituents being felspars, of which the author distinguishes three series differing in age. The typical rock is that from the Tonsen Aas (analysis II), |
