H.J. ZWART; P. HARTMAN; A. C. TOBI. To Professor Dr. Emile den Tex - on the occasion of his retirement from the chair of Petrology, Mineralogy and Crystallography, which he held at the State Universities of Leiden (since 1959) and Utrecht (1978-1983). Netherlands Journal of Geosciences, p. 129-130, 1 Jan. 1984.