The Structure of Reyerite, (Na,K)2Ca14Si22Al2O58(OH)8.6H2O

Stefano Merlino
Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 56100 Pisa, Italy

Abstract: The crystal structure of reyerite, (Na,K)2Ca14Si22Al2O58(OH)8.6H2O, Z = 1, was refined in the space group P3¯, a = 9.765, c = 19.067Å, to R = 0.064 for 1540 reflections. The structure is composed of the following structural units: (a) tetrahedral sheets S1, with composition (Si8O20)8−, characterized by six-membered rings of tetrahedra; (b) tetrahedral sheets S2, characterized by six-membered rings of tetrahedra, with six tetrahedra pointing in one direction and two pointing in the other direction—the apical oxygens of these two tetrahedra connect two inversion-related S2 sheets to build S2S¯2 double sheets, with composition (Si14Al2O38)14− and ordered distribution of aluminum cations; (c) sheets O of edge-sharing calcium octahedra. The various structural units are connected through corner sharing according to the schematic sequence …O¯S1OS2S¯2O¯…; the corresponding composition is [Ca14Si22Al2O58(OH)8]2−. The charge balance is restored by alkali cations which are placed, together with water molecules, in the cavities of the structure at the level of the double tetrahedral sheet.

Keywords: reyerite • crystal structure • calcium silicates • Niakornak • Greenland

Mineralogical Magazine; April 1988 v. 52; no. 365; p. 247-256; DOI: 10.1180/minmag.1988.052.365.12
© 1988, The Mineralogical Society
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