Abstract
A glass of composition NaAlSi3O8 with small contents of Fe has been crystallized in the presence of water vapor under 1000 bars, at temperatures in the range of 250 to 700° C for varying periods of time. The synthetic crystals were investigated microscopically and by x-ray powder diffraction methods. Most of the crystals are twinned according to the albite law, but other twins are found too. Size and form of the crystals seem to depend on the temperature of crystallization. The optic axial angles (2V x ) of the albites being measurable on the universal stage are in the range of 50 to 100 degrees. There seems to exist a linear relation between the 2ϑ131−2ϑ1¯31 values (used as an indicator for the degree of ordering) and the 2V x values. The change of the lattice parameters from albite (D) to albite (O) is suggested to deviate slightly from linearity.
In contrast to previous investigations the steady value of 2ϑ131−2ϑ1¯31 which is characteristic of the temperature of crystallization was reached more rapidly. These results suggest that small content of Fe in the glass had a catalytic effect on the Al/Si ordering.
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Herrn Dr. F. Seifert (Ruhruniversität Bochum) danken wir herzlich für die Einweisung in die experimentellen Untersuchungsmethoden sowie für manchen kritischen Hinweis. Danken möchten wir auch Herrn Dr. P. K. Hörmann für die Kontrolle der chemischen Zusammensetzung des Albitglases sowie Herrn Dr. C. W. Burnham (Harvard University) für die Bereitstellung des Rechenprogramms. Nicht zuletzt danken wir Herrn Prof. Dr. F. Karl für die kritische Durchsicht des Manuskriptes.
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Raase, P., Kern, H. Über die Synthese von Albiten bei Temperaturen von 250 bis 700° C. Contr. Mineral. and Petrol. 21, 225–237 (1969). https://doi.org/10.1007/BF00371752
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DOI: https://doi.org/10.1007/BF00371752