On 16 June 2022, our Honorary Member Egon Althaus passed away in his 90th year.

Egon Althaus was born on 15 February 1933 in Hagen, Germany. From 1953 to 1959, he studied chemistry at the University of Marburg before switching to mineralogy in 1957, graduating with a diploma in October 1959. Only sixteen months later, he received his doctoral degree (Dr. phil.) in Marburg. He completed his habilitation in mineralogy at the University of Göttingen in late 1967, where he had served as Senior Assistant from 1964 and later as Academic Councillor. Between 1968 and 1969, he worked with Phil Orville at Yale University in the United States before accepting a personal chair in Mineralogy and becoming Director of the Institute of Mineralogy at the University of Karlsruhe. From 1972 until his retirement in 2001, he held the Chair of Mineralogy in Karlsruhe, supervising more than thirty doctoral students during this time.

At the University of Karlsruhe, Egon Althaus served as Dean from 1972 to 1974 and as Vice President from 1981 to 1989. He was Deputy Speaker of several Collaborative Research Centres, served as a reviewer for the German Research Foundation (DFG) from 1976 to 1984, and was President of the German Mineralogical Society (DMG) from 1977 to 1978. He also served as editor of two mineralogical journals. Following his role as coordinator of the German Continental Deep Drilling Program (KTB) between 1985 and 1995, he played a key role in the establishment of the GFZ German Research Centre for Geosciences in Potsdam. From its founding in 1992 until 1998, he chaired the Scientific Advisory Board and had a major influence on the institute's scientific direction.

During his habilitation under H. G. F. Winkler in Göttingen, Egon Althaus focused on experimental petrology. The determination of the invariant point in the Al₂SiO₅ system remains closely associated with his name. He recognized at an early stage the importance of fluid phases in rock formation. In Karlsruhe, his students benefited greatly from the close collaboration with physical chemistry, making fluid-phase thermodynamics a major research focus. He inspired generations of students through his enthusiasm, honesty, and integrity. During the years of the KTB project, his interest increasingly turned to the petrophysical properties of rocks under the influence of fluids at high pressures and temperatures. In the later stages of his career, he devoted himself to archaeometry and the preservation of historically significant buildings.

Egon Althaus received numerous honors throughout his career. In 1998, he was awarded the Hans Stille Medal of the German Geological Society (DGG). He became a full member of the Heidelberg Academy of Sciences and Humanities in 1990 and was elected a member of Academia Europaea. In 1995, he received an honorary doctorate from the Faculty of Civil Engineering of the Budapest University of Technology. He organized the 50th Annual Meeting of the DMG in 1972, and at the 2004 Annual Meeting in Karlsruhe he was elected an Honorary Member of the Society. As early as 1975, the phosphate mineral althausite was named in his honor.

We will honor his memory with deep gratitude.

H.-G. Stosch ∙ Karlsruhe & G. Franz ∙ Berlin