Societies and Academies

Abstract

LONDON.Mineralogical Society, June 16.-Piof. H. A. Miers F.R.S., president, in the chair.-A nickel-iron alloy (Fe5Ni.,) common to the meteoric iron of Youndegin and the meteoric stone of Zomba: L. Fletcher. In the case of the Zomba meteoric stone, the gradual increase of nickel in the residue after repeated extraction of the nickel-iron with mercuric ammonium chloride was previously attributed to rusting. It is now explained by the presence in the nickel-iron of a component not easily affected by the mercuric solution and containing 38'5o per cent, of nickel. This component is identical with the "tfenite,"containing about the same percentage of nickel, which was separated from the Youndegin iron by its insolubility in dilute hydrochloric acid.-Kaolinisation and other changes in West of England rocks: F. H. Butler. The author pointed out that the gaseous emanations of a granitic magma, which are carried upwards and discharged externally, gradually bring about considerable pneumatolytic changes. Notable among these are increased vesicularity in the quartz of the peripheral part of granitic intrusions and their offsets, the elvans, also the assumption by that mineral of the idiomorphic form, and the production of tourmaline. The occurrence of tourmaline in rocks exemplifying various stages in metasomatism indicates long-continued supply of boron compounds from abysmal regions. The primary, usually brown, tourmaline in the altered acidic rocks is commonly found to have been eroded, doubtless owing to alkalinity of the kaolinising solution, before dekaolinisation and the consequent formation of acicular schorl ushered in a final deposition of quartz. The view of Prof. Vogt and other authorities that kaolinisation was effected by the rise of solutions of carbon dioxide from among calciferous rocks receives support from the occurrence of calcium sulphate in underground waters and of numerous calcium compounds in mineral veins and lodes. The unchanged condition of some topaziferous granite is one of various indications that the action of hydrofluoric acid on rocks has been low down rather than superficial. It or hydrofluosilicic acid appears to have played a part in the following sequence of events in the west of England:-(i) Decomposition of deep-seated calcite-bearing rocks, and consequent kaolinisation of neighbouring granite by evolved carbon dioxide; (2) local and variable dekaolinisation, fluorisation, and tourmalinisation of china-clay rock and china-stone by borated waters carrying dissolved fluor-spar, resulting in the formation of schorlaceous rocks and greisen. (3) Lastly, supply to the metasomatised rocks of tinstone and wolfram from solution, and then of silica. The author concluded with a brief summary of facts subversive of the popular notion that the kaolin of commerce is the result of subaerial action upon granite.-Schwartzembergite, and the drawing of light-figures: G. F. Herbert Smith. The author described the crystals occurring on three specimens in the British Museum, the locality being San Rafael, Chili. They are formed of four low pyramids, above and below, eight in all, with nearly square contour, the angle from the centre averaging 20°, with range 15°-25°, and simulate tetragonal symmetry; steep pyramids are occasionally present also. The mean refraction is 2-350. The optical characters are remarkable; through each pyramid face appears in convergent light a biaxial interference-figure (2E = 16°) with negative birefringence, the axial plane being parallel to the edge of the contour, but through intermediate sectors appears another biaxial interference-figure with larger angle (2E = 33°), the axial plane being in this case radial; the number of different directions of single refraction in the crystal is, however, only four. The pyramids give with pin-hole object a continuous band of light. Since there was no well-defined image from which to measure, it was necessary to draw these figures direct on to a projection. The author described a camera-lucida attachment for the goniometer which would allow of the preparation of projections of different sizes and of the relative variation required by the distortion in a projection. -The chemical composition of seligmannite: G. T. Prior. The results of two analyses show that this new mineral from the Binnenthal is a sulph-arsenite of copper and lead (PbCuAsS3) corresponding to the sulph-antimonite, bournonite, with which it is crystallographically similar.