Titre du document / Document title

Structural relationships between sicherite, marrite, freieslebenite, and diaphorite: analysis based on anionic nets and polyhedral characteristics

Auteur(s) / Author(s)

BERLEPSCH Peter ; MAKOVICKY Emil ; ARMBRUSTER Thomas ;

Résumé / Abstract

The crystal structures of sicherite TlAg²(As,Sb)³S⁶, freieslebenite PbAgSbS³, marrite PbAgAsS³, and diaphorite Pb²Ag³Sb³S⁸ all can be understood as superstructures of the PbS archetype with cations forming distorted MeS⁶ (Me = Tl, Ag, As, Sb, Pb) octahedra. Structural relationships between the four minerals are discussed on the basis of anionic nets and polyhedral characteristics. In order to deal with more reliable crystallographic data, a refinement of the crystal structure of marrite has been performed: space group P2¹/c, a = 5.9970(7), b = 12.6168(21), c = 7.2633(16)Å, β = 91.23 (1)° (R¹ = 2.93 % for 1176 unique reflections with I > 2 σ^I). The (100)^PbS anionic nets of underlying archetype, used for the structural comparison, consist of two different network building units: the lozenge and the trapezoid. Variations in the mutual arrangements of lozenges and trapezoids lead to the different structures treated in this study. These structures reflect both different chemical compositions and space demand as well as a satisfactory bond valence balance for sulphur. Calculated geometrical values related to the coordination polyhedra of the four structures include the polyhedral volumes (V^p), the sphere volumes V^s of the spheres least-squares fitted to the ligands of individual coordination polyhedra, the volume eccentricity (ECC^v), the volume sphericity (SPH^v), and the volume distortion v.

Revue / Journal Title

Neues Jahrbuch für Mineralogie. Abhandlungen   ISSN 0077-7757   CODEN NJMIAK 

Source / Source

2002, vol. 178, n^o1, pp. 75-91 [17 page(s) (article)]

Langue / Language

Anglais
Revue : Multilingue

Editeur / Publisher

Schweizerbart, Stuttgart, ALLEMAGNE  (1950) (Revue)

Localisation / Location

INIST-CNRS, Cote INIST : 925 A, 35400010752377.0040