Abstract
LONDON. Mineralogical Society, Mar. 19.—A. W. Groves and A. E. Mourant: Inclusions in the apatities of some igneous rocks. Apatite crystals with dark cores of inclusions have been observed among the heavy minerals of some English sedimentary rocks, but there are few records of such apatites in igneous rocks. The authors record several such occurrences in granites and in volcanic rocks from Normandy, Jersey, and Brittany. Five different types are distinguished in the granite of northern Brittany alone. In one type with a definitely pleochroic core the inclusions appear to consist of biotite or chlorite, but in other types it has not been possible to determine their nature.—L. A. Narayana Iyer: Calc-gneisses and cordierite-sillimanite-gneisses of Coimbatore, Madras Pres., and similar occurrences in India. The paper dealt with a suite of crystalline gneisses in the ancient Archaean complex of India of Dharwar age (Huronian), consisting of the above two facies, which are in close association. Similar suites of rock occur in different parts of India, forming a definite stratigraphic horizon. The author considers their formation as due to thermal or ‘infra-plutonic’ metamorphism followed or accom panied by regional or dynamo-thermal metamorphism of pelitie schists and calcareous sediments.—F. A. Bannister: A relation between the density and re fractive index of silicate glasses with application to the determination of imitation gem-stones. The study of simple glass families leads to a relation between the refractive index and density which can be applied in a modified form to the determination of imitation gem-stones, (n-N)/(d - D), where N and D are the refractive index and density of silica glass, is plotted against n by a simple graphical method, whereupon the various imitations separate into groups; the members comprising any one group are chemically similar. Doubtful cases can be solved by measuring in addition the relative dispersion.—H. E. Buckley: The crystallisation of potash-alum. The author described the results of experiments on the differences of crystal habit obtained under varying conditions of cooling and evaporation, and in the presence of various substances in solution such as strong acids, AlCl3, FCl3, amyl alcohol, Bismarck Brown, etc.
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Societies and Academies. Nature 123, 589–591 (1929). https://doi.org/10.1038/123589b0
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DOI: https://doi.org/10.1038/123589b0