Stephen Aja

Education:

Ph.D., Washington State University - 1989 (Geology)

Areas of Expertise:

Our research activities deal with various aspects of the thermodynamics of clay mineral-water interactions. Clay minerals are major component of minerals near the earth's surface. Clay mineral studies are applicable to petroleum reservoir quality, carbon sequestration in geologic formations, and formation of some ore minerals. Also, the discovery of clay minerals on the surface of Mars intersects with our research interests.

Books and Publications

Aja, S. U. (2021) Resolving the conundrum of equilibrium solubility of smectites. American Mineralogist, In Press. DOI: https://doi.org/10.2138/am-2022-8213 (Books and Publications: Article (Peer-reviewed)) 2021

Aja, S.U.On the thermodynamic stability of illite and I-S minerals. Clays Clay Miner. (2020). https://doi.org/10.1007/s42860-019-00044-x

https://rdcu.be/b1I4q
(Books and Publications: Article (Peer-reviewed)) 2020

Aja, S. (2019) Excess functions of chlorite solid solutions and neoformation of Fe-chlorites: Some implications of recent thermochemical measurements. American Mineralogist, 104, 232 - 243


http://www.minsocam.org/MSA/AmMin/Public_Access/2019_public/AM104P0232.pdf
(Books and Publications: Article (Peer-reviewed)) 2019

Aja, S. U. and Cranganu, C. Exploring the Earth System, 2nd edition, Kendall-Hunt Publishing Co, Dubuque, IA. (Books and Publications: Book (Authored)) 2017

Aja, S. Omotoso, O., Bertoldi, C., Dachs, E. and Benisek, A. (2015) The structure and thermochemistry of three Fe-Mg chlorites. Clays and Clay Minerals, 63, 351-367. (Books and Publications: Article (Peer-reviewed)) 2015

Aja, S.U. and C. Crânganu. Exploring the Earth System. Dubuque, Iowa: Kendall-Hunt. (Books and Publications: Book (Authored)) 2013

Aja, S.U (2002) The stability of Fe-Mg chlorites in hydrothermal solutions: II. Thermodynamic properties. Clays and Clay Minerals, Vol. 50, No. 5, 591-600. (Books and Publications: Article (Peer-reviewed)) 2002

Aja, S.U and Dyar, M. D. (2002) The stability of Fe-Mg chlorites in hydrothermal solutions - I. Results of experimental investigations. Applied Geochemistry, 17, 1219-1239. (Books and Publications: Article (Peer-reviewed)) 2002

Kulik, D.A., Aja, S.U., Sinitsyn, V.A. and Wood, S.A. (2000) Acid-base surface chemistry and sorption of lanthanides on K+-saturated Marblehead illite: II. A multisite surface complexation modeling. Geochimica et Cosmochim Acta, Vol. 64, No. 2, pp. 195-213. (Books and Publications: Article (Peer-reviewed)) 2000

Sinitsyn, V.A., Aja, S.U., Kulik, D.A. and Wood, S.A. (2000) Acid-base surface chemistry and sorption of lanthanides on K+-saturated Marblehead illite: I. Results of an experimental investigation. Geochimica et Cosmichimica Acta, vol. 64, no. 2, pp. 184-195 (Books and Publications: Article (Peer-reviewed)) 2000

Aja, S. U . and Small, J.S. (1999) The solubility of a low-Fe clinochlore between 25 and 175 °C and Pv = PH2O. Eur. J. Mineral., 11, 829-842 (Books and Publications: Article (Peer-reviewed)) 1999

Aja, S.U. (1998) The sorption of the rare earth element, Nd, onto kaolinite at 25 °C. Clays and Clay Minerals, vol. 46, No. 1, 103-109 (Books and Publications: Article (Peer-reviewed)) 1998

Aja, S.U and Kulik, D.A. (1997) An integrated model of equilibrium solubility and sorption of some lanthanides by clay minerals: Application of Gibbs Energy Minimization Techniques. Program Report Prepared for Radioactive Waste Management Program Office of Central Europe and Eurasia, National Research Council/National Academy of Sciences. 138 pp. (Books and Publications: Article (Other)) 1997

Aja, S.U. (1997) An experimental investigation of the sorption of some lanthanides on Marblehead illite in aqueous KCl solutions at 25 °C. Report of Research Investigation prepared for Radioactive Waste Management Program Office of Central Europe and Eurasia, National Research Council/National Academy of Sciences. 36 pp. (Books and Publications: Article (Other)) 1997

Aja, S. U, (1995) Controls on illitization reactions: A thermodynamic approach In M.N. Oti, G. Postma (eds.) Geology of Deltas, A. A. Balkema Publishers, pp. 209 - 216. (Books and Publications: Book Chapter) 1995

Aja, S.U, Wood, S.A. and Williams-Jones, A.E. (1995) The aqueous geochemistry of Zr and the solubility of some Zr-bearing minerals. Applied Geochemistry, vol. 10, pp. 603-620 (Books and Publications: Article (Peer-reviewed)) 1995

Aja, S.U. (1995) Thermodynamic properties of some 2:1 layer clay minerals from solution-equilibration data. Eur. J. Mineral., 7, 325-333. (Books and Publications: Article (Peer-reviewed)) 1995

Aja, S.U and Rosenberg, P.E. (1992) The thermodynamic status of compositionally-variable clay minerals: A discussion. Clays and Clay Minerals, Vol. 40, No. 3, 292-299 (Books and Publications: Article (Peer-reviewed)) 1992

Aja, S.U., Wood, S.A. and Williams-Jones, A.E. (1992) On estimating the thermodynamic properties of silicate minerals. Eur. J. Mineral., 4, 1251-1263. (Books and Publications: Article (Peer-reviewed)) 1992

Aja, S.U, Rosenberg, P.E. and Kittrick, J.A. (1991) Illite equilibria in solutions: II. Phase relationships in the system K2O-Al2O3-MgO-SiO2-H2O. Geochimica et Cosmochimica Acta, Vol. 55, pp. 1365-1374. (Books and Publications: Article (Peer-reviewed)) 1991

Aja, S.U., Rosenberg, P.E and Kittrick, J.A. (1991) Illite equilibria in solutions: I. Phase relationships in the system K2O-Al2O3-SiO2-H2O between 25 and 250 °C. Geochimica et Cosmochimica Acta, Vol. 55, pp. 1353-1364. (Books and Publications: Article (Peer-reviewed)) 1991

Rosenberg, P.E., Kittrick, J.A. and Aja, S.U. (1990) Mixed-layer illite/smectite: A multiphase model. American Mineralogist, Vol. 75, pages 1182-1185. (Books and Publications: Article (Peer-reviewed)) 1990

Conferences, Seminars and Symposiums

The thermodynamic stability of clay minerals: A retrospective In Program & Abstracts, 55th Annual Meeting of the Clay Minerals Society. University of Illinois, Urbana-Champaign, June 11-14, 2018. (Conferences, Seminars and Symposiums: Invited Talk) 2018

Chlorite thermochemistry: Insights from combining calorimetric and solution equilibration data. 53rd Annual Meeting of the Clay Minerals Society, June 5-8, 2016. Atlanta, Georgia. (Conferences, Seminars and Symposiums: Conference Presentation) 2016

"A ternary solid solution model of natural chlorites". 2015 Geological Society of America Annual Meeting. Baltimore, MD. November 4. (Conferences, Seminars and Symposiums: Conference Presentation) 2015

Kulik, D. A. and Aja, S. U. (1997) The hydrothermal stability of illite: Implications of empirical correlations and Gibbs energy minimization. Proceedings of the Fifth International Symposium on Hydrothermal reactions. Gatlinburg, Tennessee. July 20-24, 1997. (Conferences, Seminars and Symposiums: Contributed Talk) 1997

Aja, S.U., Wood, S.A. and Williams-Jones, A.E. (1993) Synthesis and solubility of neodymium hydroxybastnaesite In Proceedings of the 4th International Symposium on hydrothermal reactions, eds. M. Cuney and M. Cathelineau, pp. 3-6, Vandoeuvre-les-Nancy, France. (Conferences, Seminars and Symposiums: Conference Presentation) 1993