Hatten Yoder, experimental petrologist, Honorary Fellow and winner of the Society’s Wollaston Medal, died on 2 August 2003 after complications following surgery. Yoder was emeritus director of the Carnegie Institution of the Washington Geophysical Laboratory.
Yoder graduated from the University of Chicago in 1949 and got his PhD at MIT in 1948. He subsequently received many honours, including honorary doctorates from the University of Paris IV (1981) and the Colorado School of Mines (1995). As well as this Society, he held honorary fellowships at nine professional, national and international associations.
The research he carried out underpins the way in which we understand the physicochemical processes of igneous rock formation today, for he was a pioneer in modern experimental petrology and geochemistry. His early studies included work on the high-pressure stability of jadeite, micas and sulphide minerals, but though the subject matter varied through his career, his preferred tool was always the high-pressure high temperature laboratory.
When he arrived at the Carnegie Washington Geophysical Laboratory, Yoder set about designing pieces of equipment that could simulate conditions in the deep crust and uppermost mantle. This equipment, still in use today, allowed him to make his early discoveries (with Eugster and J V Smith) about stability relations of micas, and to carry out detailed studies of the melting of phlogopite (with Ike Kushiro, who himself won the Wollaston Medal in 2003).
Yoder’s phlogopite work furnished the basic principles that control the melting of other hydrous minerals at high pressure. It was his continuing fascination with the role of water, and phase relations in water-bearing systems, which led him (in 1968) to the then revolutionary conclusion that water played a crucial role in high-pressure magmatism in the upper mantle.
Following in the footsteps of Norman Bowen and others, Yoder’s work on silicate melting systems through the 1950s culminated in his contribution (with Tilley, 1962) over 192 pages of the Journal of Petrology, where the graphical tool now known to all as the "basalt tetrahedron" was first brought before the geological world.
Yoder was married for 42 to years to Elizabeth Marie (d. February 2001). His son, Hatton S Yoder III, died in 1998. He is survived by his daughter Karen M Yoder Wallace, and granddaughter Brianna Elizabeth Wallace.
Ted Nield, after Bjorn Mysen Carnegie Istitution, Washington DC