THE MIXING PROPERTIES OF MELTS IN THE SYSTEM NAALSI2O6-KALSI2O6 DETERMINED BY KNUDSEN CELL MASS-SPECTROMETRY
The activities of the NaAlSi2O6 and KAlSi2O6 components in this system have been determined at 1150o-1530oC. Mixing is close to ideal despite dissimilar crystal structures; this may reflect a re-organization of the melt in Na-rich compositions to give NaAlSiO4-like and SiO2-like constituents nearer...
| Main Authors: | , , |
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| Format: | Journal article |
| Language: | English |
| Published: |
1983
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| Summary: | The activities of the NaAlSi2O6 and KAlSi2O6 components in this system have been determined at 1150o-1530oC. Mixing is close to ideal despite dissimilar crystal structures; this may reflect a re-organization of the melt in Na-rich compositions to give NaAlSiO4-like and SiO2-like constituents nearer the cage structure of nepheline than the chain structure of jadeite and with Al in tetrahedral rather than octahedral coordination. The partial molar heats and excess entropies of mixing show a pronounced minimum at Na:K = 3:1 which compares closely with the normal composition of nepheline. This may be an example of a more general phenomenon, in which liquids tend to approximate the structure of the crystalline phase stable on the liquidus at the particular composition, rather than that of a mineral having the same composition as the melt.-R.A.H. |
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