On the entropy of glaucophane Na2Mg3Al2Si8O22(OH)2 |
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Authors: | Richard A Robie Bruce S Hemingway Philippe Gillet B Reynard |
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Institution: | (1) U.S. Geological Survey, 22092 Reston, VA, USA;(2) Institut de Géologie, Université de Rennes, 35042 Rennes Cedex, France |
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Abstract: | The heat capacity of glaucophane from the Sesia-Lanza region of Italy having the approximate composition (Na1.93Ca0.05Fe0.02) (Mg2.60Fe0.41) (Al1.83Fe0.15Cr0.01) (Si7.92Al0.08)O22(OH)2 was measured by adiabatic calorimetry between 4.6 and 359.4 K. After correcting the C
p
0
data to values for ideal glaucophane, Na2Mg3Al2Si8O22(OH)2 the third-law entropy S
298
0
-S
0
0
was calculated to be 541.2±3.0 J·mol-1·K-1. Our value for S
298
0
-S
0
0
is 12.0 J·mol-1·K-1 (2.2%) smaller than the value of Likhoydov et al. (1982), 553.2±3.0, is within 6.2 J·mol-1·K-1 of the value estimated by Holland (1988), and agrees remarkably well with the value calculated by Gillet et al. (1989) from spectroscopic data, 539 J·mol-1·K-1. |
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