It is with great sadness that I share the news that Robert Day Shannon passed away peacefully at home on Sunday, May 31, at the age of 90 with his family at his side. Bob was a leading scientist in the area of solid-state chemistry and crystal chemistry with a strong background in mineralogy. As a research chemist at the Experimental Station of E.I. Du Pont de Nemours in Wilmington, Delaware, USA, he was responsible for various research projects, resulting in many patents and publications which attracted world-wide attention. He has more than 140 publications which were cited nearly 90,000 times according to the Web of Science (June 2026). Just his paper on ionic radii in Acta Crystallogr. 1976 has been cited more than 65,000 times. Bob was born on August 28, 1935, in Highland Park, Michigan, USA. He received his Master degree in Ceramic Engineering from the University of Illinois in 1959, and his Ph.D. in 1964 from the University of California at Berkeley. In the same year he started as a research chemist at Du Pont in Wilmington, Delaware, where he retired in 1992. In this period, he spent a sabbatical leave 1971-1972 at McMaster University studying crystal structures of vanadates and bond-strength relations in oxides, continuing these studies 1972-1973 at University of Grenoble, France. From 1982 to 1983 he worked at the Institut de Recherches sur la Catalyse in Lyon, France, studying the crystal chemistry of zeolites. When he returned to Wilmington, it was my pleasure to join his group doing research on zeolites. I got to know an exceptionally hardworking scientist and a wonderful, kind person who was always willing to help in any situation. Bob was a member of various scientific societies and a fellow of the Mineralogical Society of America. In 1993, he received the Humboldt Research Award which is one of the highest ranked awards in Germany. He spent a full year at Universities of Mainz and Bremen to study the electronic polarizabilities of cations and anions to predict refractive indices of minerals and inorganic compounds. This work will be continued and brought to completion in his spirit. The mineral bobshannonite, Na_2 KBa(Mn,Na)_8 (Nb,Ti)_4 (Si_2 O_7 )_4 O_4 (OH)_4 (O,F)_2 from Mont Saint-Hilaire, Québec, Canada, was named in his honor. After retiring, he moved with his wife Cookie to Boulder, Colorado, where they settled into a house high up in the mountains. He lived there until he passed away a few days ago. We will always keep him in our memories. Reinhard X. Fischer -- Prof. Dr. Reinhard X. Fischer Fachbereich Geowissenschaften der Universität Klagenfurter Straße 2 28359 Bremen Tel. (421) 218-65164 FAX (421) 218-65189 Sek. (421) 218-65161