2013/02/01 by Luca Bindi, Nicholas E. Pingitore · 1 citation
Materials Science · Earth and Planetary Sciences · Physics and Astronomy · Chemistry · #Crystal Structures and Properties #Mineralogy and Gemology Studies #Advanced Condensed Matter Physics #Orthorhombic crystal system #Monoclinic crystal system #Isostructural #Crystallography #Crystal structure #Chemistry #Mineral #Crystal chemistry
paper · doi:10.1180/minmag.2013.077.1.03
openalex publication_date 2013/02/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/11
Abstract An examination of a specimen of aguilarite from the type locality provides new data on the chemistry and structure of this mineral. The chemical formula of the crystal used for the structural study is (Ag 3.98 Cu 0.02 )(Se 0.98 S 0.84 Te 0.18 ), on the basis of 6 atoms. The mineral was found to be monoclinic, crystallizing in space group P 21 /n , with a = 4.2478(2), b = 6.9432(3), c = 8.0042(5) Å , β = 100.103(2)º, V = 232.41(2) Å 3 and Z = 4. The crystal structure [refined to R 1 = 0.0139 for 958 reflections with I > 2 σ ( I )] is topologically identical to that of acanthite, Ag 2 S. It can be described as a body-centred array of tetrahedrally coordinated X atoms ( X = S, Se and Te) with Ag2 X 3 triangles in planes nearly parallel to (010); the sheets are linked by the Ag1 silver site, which has twofold coordination. Aguilarite is definitively proved to be isostructural with acanthite; it does not have a naumannite-like structure, as previously supposed. Our data support the hypothesis that there are two solid solution series in the system: a monoclinic 'acanthite-like' series (from Ag 2 S - Ag 2 S 0.4 Se 0.6 ), and an orthorhombic 'naumannite-like' series (from Ag 2 S 0.3 Se 0.7 -Ag 2 Se). This is supported by data gathered on synthetic counterparts. Aguilarite remains as a valid as a mineral species, but it should be described as the Se-analogue of acanthite. In this study we also (1) review the history of the aguilarite; (2) compare properties of synthetic and natural aguilarite; and (3) demonstrate how earlier researchers erred in describing aguilarite as orthorhombic. The Te-bearing composition of the studied aguilarite crystal suggests the possibility of a solid solution with cervelleite (Ag 4 TeS).