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A tribute to Hal Helgeson on his 70th birthday


Geochimica et Cosmochimica Acta, issue 21, volume 65


Geochemistry(15%), Health safety and environment(14%)


This issue of Geochimica et Cosmochimica Acta is dedicated to Harold Helgeson on the occasion of his 70th birthday. Together with Dimitri Sverjensky, Eric Oelkers, and all who contributed to this special issue of Geochimica, we wish to acknowledge the great difference it has made to us to know Hal, to work with him, or to have been inspired by his example over the years.

Those who meet Hal rarely forget the experience. He is widely known to the geochemical community for his innovation, rigor, farsightedness, and tenacity in the application of thermodynamics and kinetics to the study of geochemical processes. He is known to his friends and close colleagues for his great generosity, honesty, fierce loyalty, diverse opinions, and unconventional sense of humor. Hal can also be a formidable challenge. Once, after a presentation at an international meeting, he asked the speaker, “Do you actually expect any of us to believe any of this?” Over the years, this speaker has been in noteworthy company. Evidently, there is no dilute version of Hal. He tackles research and life with an enthusiasm and at an energy level that can exhaust all but a few full-time fellow contestants. As a result, his influence on the development of theoretical geochemistry is profound, unique, and monumental.

In the 1960’s, Hal pioneered the use of computers to calculate the speciation of major, minor, and trace elements in hydrothermal ore-forming fluids at high pres

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