The Crystal Structure of Cesanite, Ca1+xNa4−x(SO4)3(OH)x · (1 − x)H2O, a Sulphate Isotypic to Apatite

V. Tazzoli
Centro di Studio per la Cristallografia Strutturale del CNR c/o Istituto di Mineralogia dell'Universita', Via Bassi, 4-27100 Pavia, Italy

Abstract: Cesanite, Ca1+xNa4−x(SO4)3(OH)x · (1 − x) H2O, is hexagonal, space group P63/m, a = 9.446(1) and c = 6.895(1) Å, Z = 2. The crystal structure refinement, carried out by utilizing 457 independent reflections (final R = 0.021), shows that cesanite is isotypic to hydroxyapatite. The P atom of apatite is completely replaced in cesanite by an S atom; the two independent Ca sites of apatite are occupied respectively by Na and Na + Ca, the charge balance being by partial substitution of H2O for OH although the occupancy of the (H2O,OH) sites is not complete. The relationship between the water vacancies and the structural features of the (Ca,Na) polyhedron is discussed. A new general formula for the apatite-wilkeite-ellestadite series is proposed.

Mineralogical Magazine; March 1983 v. 47; no. 342; p. 59-63; DOI: 10.1180/minmag.1983.047.342.10
© 1983, The Mineralogical Society
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