Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) An erratum has been published Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hovis, G. L. Articles by Gottschalk, M. Search for Related Content GeoRef GeoRef Citation

Solution calorimetric determination of the enthalpies of formation of NH₄-bearing minerals buddingtonite and tobelite

¹ Department of Geology and Environmental Geosciences, Lafayette College, Easton, Pennsylvania 18042-1708, U.S.A.
² GeoForschungsZentrum-Potsdam, Telegrafenberg, D-14473 Potsdam, Germany

Correspondence: ^* E-mail: hovisguy{at}lafayette.edu

Enthalpies of solution of the NH₄⁺-bearing minerals buddingtonite (NH₄AlSi₃O₈ feldspar) and tobelite [NH₄Al₂(AlSi₃O₁₀) (OH)₂ mica] have been measured in 20.1 wt% hydrofluoric acid (HF) at 50°C. Utilizing additional HF solution calorimetric data from this laboratory for sanidine, albite, muscovite, paragonite, halite, sylvite, salammoniac, gibbsite, and water, along with enthalpies of formation from Robie and Hemingway (1995) for the same phases, the heats of formation at 298.15 K of buddingtonite and tobelite have been determined to be –3883.9 and –5881.3 kJ/mol, respectively. Entropies of ~247 and ~319 J/(mol ·K) for these minerals (298.15 K) have been approximated from various ion-exchange equilibria involving feldspars, micas, and chlorides. Collectively, these data result in 298.15 K Gibbs free energies of formation from the elements of –3579 and –5422 kJ/mol, respectively, for buddingtonite and tobelite, values that differ by 40 to 50 kJ/mol from those given previously by Mäder et al. (1996). The calculated phase equilibria that result from the data of this investigation are reasonable relative to the conditions required to synthesize both buddingtonite and tobelite (Harlov et al. 2001b, 2001c).

This article has been cited by other articles:

				G. L. Hovis, J. R. Morabito, A. Spooner, A. Mott, E. L. Person, C. M. B. Henderson, J. Roux, and D. Harlov A simple predictive model for the thermal expansion of AlSi3 feldspars American Mineralogist, October 1, 2008; 93(10): 1568 - 1573. [Abstract] [Full Text] [PDF]