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A dispersion method of determining plagioclases in cleavage-flakes

Published online by Cambridge University Press:  14 March 2018

Seitarô Tsuboi
Seitarô Tsuboi*
Affiliation:
Of the Geological Institute, Imperial University of Tokyo, Japan
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Extract

Recently H. E. Merwin employed an improved immersion method for determining refractive indices to identify certain salts of the system Fe2O3–SO3–H2O. In the present paper is described an application of the principle of his method to the determination of plagioclases in cleavage-flakes.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 20 , Issue 102 , September 1923 , pp. 108 - 122
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1923

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References

Page 108 note 1 Posnjak, E. and Merwin, H. E., Journ. Amer. Chem. Soc., 1922, vol. 44, p. 1970.Google Scholar

Page 108 note 2 i.e. refractive indices for two or more different wave-lengths.

Page 109 note 1 Eskola, P., Journ. Geol. Chicago, 1922, vol. 30, p. 265 CrossRefGoogle Scholar.

Page 109 note 2 Finely crushed grains of plagioclases are mostly cleavage-flakes

Page 109 note 3 Tsuboi, S., Journ. Geol. Soc. Tokyo, 1920, vol. 27, p. 892 Google Scholar. The diagram was reproduced in A. Johannsen, ‘Essentials for the Microscopical Determination of Rock-forming Minerals and Rocks.’ Chicago, 1922, folding table.

Page 111 note 1 Becke, F., Tscherm. Min. Petr. Mitt., 1894, vol. 14, p. 430.Google Scholar

Page 113 note 1 The dispersion data for the albite-oligoelase from Bakersville determined by C. Viola (Zeits. Kryst. Min., 19007 vol. 327 p. 336) have not been adopted because they contained conflicting data. The value of n 2 should be greater than that of β (S. Tsuboi, Journ. Geol. Soc. Tokyo, 1918, vol. 25, p. 39 ; Journ. Coll. Sci. Imp. Univ. Tokyo, 19207 vol. 43, art. 6, p. 63), while n 2 for b (010) obtained from Viola's data is less than β.

Page 115 note 1 S. Kôzu determined the relative dispersion of the optic axes of these anorthites (Tables X-XI) and calculated ϕ, λ, ϕ′, and λ′ assuming that the orientation of tile optic axis B for sodium-light is the same as that in the anorthite from Vesuvius. (F. Becke, Sitzungsber. Akad. Wiss. Math.-naturw. Kl. Wien, 1899, Abt. I, vol. 108, p. 437.)

Page 118 note 1 By (n1–n1 D)l,, &c., are meant the difference between n 1 for the light of a given wave-length and n 1 for sodium-light in b (010), &c.

Page 118 note 2 The refractive indices for 687 μμ of the albite from the Island of Crete (Table XIII) were omitted because they are evidently too low, as can be found by drawing the dispersion curves for this felspar.

Page 119 note 1 The maximum deviation of any of the interpolated central values for n 1 and n 2 (both in b and c) from the corresponding point on the curve in the diagram is ±0.0002.

Page 120 note 1 A mixture of cassia oil and clove oil, roughly 1 : 2 in volume, had the dispersion represented by DAE.

Page 120 note 2 Under favourable conditions differences less than 0.0002 in refractive indices between liquid and mineral can be detected. (Cf. Merwin, loc. cit.)

Page 121 note 1 Larsen, E. S., Bull. U.S. Geol. Survey, 1921, no. 679, p. 14.Google Scholar

Page 121 note 2 It is not necessary to determine the dispersion of every immersion medium. If the dispersion of cassia oil and clove oil is determined, the dispel~ion of any mixture of these two oils can be found graphically as follows :—Along the right and left margins of a cross-section paper, mark the refractive indices for light of various wave-lengths of cassia and clove oils respectively, and connect the points representing a given wave-length. Determine n D of a certain mixture of these two oils; mark it on the connecting line for sodium-light ; and draw a vertical line through n D. Then the dispersion of the mixture can be read from the intersections of this vertical line with the connecting lines for different wave-lengths.