Die Beziehungen zwischen der chemischen Zusammensetzung,Lichtbrechung und Dichte einiger koexistierender Biotite,Muskowite und Chlorite aus granitischen Tiefengesteinen

From 19 granitic rock samples the coexisting biotites, muscovites, and chlorites were separated by means of a magnetic separator as well as through hand-picking under the microscope.The measured refractive indices and densities of the biotites and of the iron-rich chlorites show stronger variations than those measured on the muscovites.These data, together with 20 complete chemical analyses of these complicated layer silicates, were used to test the applicability of the rule of Gladstone and Dale giving a simple theoretical relationship between chemical composition, density and mean refractive index of a substance.For 16 samples the theoretical densities according to Gladstone-Dale agree within 2% with the measured densities. In 4 samples of biotite and muscovite showing high contents of fluorine discrepancies up to 4% were found.This might suggest that the specific refractive energy for F in layer silicates is different from the value given by Larsen and Berman for silicates in general.The effects of substitutions of main elements Si, Al, Fe²⁺, Mg, K, Ti, Fe³⁺, Ca, and F on the refractive indices of layer silicates are shown to be very complex.

---

---

Mein Dank gilt Herrn Direktor Prof. Dr. H. R. v. Gaertner, welcher meine Untersuchungen während meiner Tätigkeit bei der Bundesanstalt für Bodenforschung, Hannover, mit Interesse förderte. Ferner danke ich den Herren Dr. W. Harre und Dr. H. Gundlach, Bundesanstalt für Bodenforschung, für die Durchführung der chemischen Mineralanalysen, sowie der Deutschen Forschungsgemeinschaft, Bad Godesberg, für ihre finanzielle Beihilfe. Meinen Assistentinnen Frau H. Grapp, Frl. B. Köhler, Frl. G. Klaetsch und Frau R. keese sei herzlich für ihren geduldigen Fleiß bei den Separierungsarbeiten gedankt.