Entropy of mixing in sanidine
Downloadable Content
Abstract
- The entropy of mixing in high-temperature alkali feldspars has been re-evaluated using
recently-published heat-of-solution data in conjunction with the results of earlier equilibrium
experiments. We find that the excess entropy of mixing is distinctly positive over most of the
K-Na composition range and most strongly so for the more potassic compositions. The excess
entropies at the sadie end of the series are much smaller and may even be slightly negative for
compositions near the N a end. The asymmetry in the excess entropy appears to be the
principal reason for the asymmetry of the alkali feldspar solvus.
Short-range K-Na ordering can only cause a negative excess entropy, hence is either
negligible or overwhelmed by other effects of opposite sign. A likely explanation is that there
is a positive excess (probably best seen at very low temperatures) in the vibrational heat
capacity, and that this effect is greatest for the more K-rich compositions. This asymmetry is
what would be expected if it is assumed that a small atom on a large-atom site would have greater vibrational freedom than a large atom on a small-atom site.
| Title | Entropy of mixing in sanidine |
|---|---|
| Creator | Thompson, J. B. |
| Hovis, Guy L. | |
| Publisher | American Mineralogist |
| Academic Department | Geology & Environmental Geosciences |
| Division | Natural Sciences |
| Organization | Lafayette College |
| Date Issued | 1979 |
| Date Available | 2013-02-11T21:27:04Z |
| Type | Article |
| Language | English |
| Bibliographic Citation | Thompson, J. B. and G. L. Hovis. (1979) "Entropy of mixing in sanidine." American Mineralogist 64 (1/2): 57-65. |
| Standard Identifier | Handle 10385/1098 |
| Permalink | http://hdl.handle.net/10385/1098 |
| Rights Statement |
In Copyright
|
| Rights Holders | Mineralogical Society of America |
Contains
| File | Hovis-AmericanMineralogist-vol64-1979.pdf | Uploaded 2019-10-20 | Public | Download |
Member of Collection
