This issue of the European Journal of Mineralogy is a Festschrift to celebrate the exceptional scientific and educational carrier of Professor Thomas Armbruster on the occasion of his retirement from the University of Bern, Switzerland. The issue collects papers written by his friends and colleagues, who wanted to honour Thomas’ achievements and to acknowledge his influence upon them in both scientific and human perspectives.

Thomas Armbruster was born in 1950 in Baden-Baden, studied at the University of Mainz and obtained his PhD at the Ruhr-University Bochum in 1977. That very same year he married Gabi Armbruster and the couple moved to the Virginia Polytechnic Institute (VPI), Blacksburg, U.S.A., where Thomas was a post-doctoral fellow with Donald Bloss, working on the crystal chemistry of cordierite. After returning to Europe in 1980, he became X-ray crystallographer and lecturer in Mineralogy at the University of Bern (Switzerland) and started his own independent and highly productive research career. He has many interests, but focused primarily on the following topics: order-disorder phenomena in mineral structures; modular aspects of mineral structures; application, properties, and structure of natural zeolites; and crystal chemistry of Mn3+-minerals. In all these areas, he made profound contributions to our understanding of the structural mechanisms underlying the complexity of structures and the behaviour of these minerals. Since 1977 Thomas Armbruster co-authored more than 330 research articles in peer-reviewed international journals as well as book chapters (with a rate of about nine articles per year). In addition, he mentored a large number of students, postdocs and younger colleagues, who keep fond memories about Thomas’ deep research insights, wise advice and good sense of humour.

The scientific achievements of Thomas Armbruster have been internationally recognized. The list of his honours include: the Dana Medal from the Mineralogical Society of America (2008); an honorary membership in the Russian Mineralogical Society (2015); and a new mineral, armbrusterite (featured on the cover of this issue), named in his honour by a humble group of Russian mineralogists and crystallographers in 2007. Thomas also made important contributions to non-mineralogical issues, for example on the history, breeding, and use of working horses in the Schwarzwald (Armbruster, T., Brodauf, W., Schröder, G., 2007–2013: “Schwarzwälder Kaltblut – Geschichte und Geschichten”, Vol. I–III, published by Schillinger Publishing House).

With the publication of this issue of EJM, the editors and the authors wish to express their gratitude and admiration to Thomas Armbruster as to an outstanding scientist and a great colleague.