Hydrothermal recrystallization and transformation of tridymite |
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| Authors: | O W Flörke K Langer |
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| Institution: | (1) Institut für Mineralogie, Ruhr-Universität Bochum, D-463 Bochum, Germany-BRD |
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| Abstract: | Well ordered tridymites containing atmost 0.016% Na (0.004% Na) were prepared at 1400° C from Na2WO4-(K2WO4-) fluxes using high purity amorphous silica as starting material. No further reduction of these Na-contents was attainable by soxhlet extraction. These tridymites were treated hydrothermally at temperatures between 815 and 950° C and 200 bars H2O. The products obtained were investigated optically as well as by powder X-ray methods and were analyzed for Na-contents: the hydrothermal treatment resulted either in recrystallization of tridymite or transformation into quartz mostly depending on Na-contents. Na-contents below about 0.015% tend to favour recrystallization of tridymite within the quartz field (<870° C), Na-contents above about 0.03% tend to favour formation of quartz within the tridymite field (>870° C). This may be due to influences of Na-traces either on the kinetics or on the equilibrium temperature of tridymite-quartz transformation. |
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