gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/002646198547459 Cation Distribution in Natural Zn-Aluminate Spinels Lucchesi S. Dipartimento di Scienze della Terra, Uuiversità di Roma “La Sapienza”, P. le A. Moro 5, 00186 Roma, Italy Della Giusta A. Dipartimento di Mineralogia e Petrologia, Università di Padova, Corso Garibaldi 37, 35122 Padova, Italy Russo U. Dipartimento di Chimica Inorganica, Metallorganica e Analitica, Università di Padova, Via Loredan 4, 35131 Padova, Italy 2 1998 62 1 41 54 3 6 1996 24 4 1997 Copyright © 1998, The Mineralogical Society 1998 Abstract

The intracrystalline cation distributions in fourteen natural Zn-aluminate spinels were determined by means of X-ray single-crystal structural refinement, supported for some samples by Mössbauer spectroscopy.

Zinc substitutes for Mg and subordinately Fe2+ and its relevant changes in content, from 0.10 to 0.96 atoms per formula unit (apfu), are not related to variations of cell parameter. The latter is determined mainly by the substitution Fe3+ ⇌ Al. In agreement with data from synthetic samples, a small but definite amount of Zn (up to 0.06 apfu) is located in the octahedral M site. Fe2+, when present, shows a preference for tetrahedral coordination.

An improved value of the tetrahedral Zn(T)-O distance (1.960 Å) was obtained, integrating the set of interatomic distances used for the determination of cation distribution in spinels.

 Keywords spinel zinc gahnite crystal chemistry intracrystalline disorder