What does this research mean for the field?

High silver content in argentotetrahedrite minerals shifts sulfur from the central S(2) site to a newly identified S(3) site, leading to the compression of the [Ag, Cu]6 octahedral cluster. Novelty: ClaimNovelty.NOVEL_FINDING. Consensus alignment: ConsensusAlignment.NEUTRAL.

June 3, 2026

Refinement of the Crystal Structure of Argentotetrahedrite: A New S(3) Site in Octahedral Cluster Ag, Cu6

Key Points

This research aims to refine the crystal structure of argentotetrahedrite and identify new sulfur sites.
Utilized electron microprobe analysis and X-ray diffraction to study minerals from the Mangazeyskoye deposit.
Refined the crystal structures of four Ag-bearing fahlore minerals using XRD methods.
Conducted quantum chemical modeling to analyze substitution effects in octahedral clusters.
Identified a new sulfur site S(3) caused by high Ag content (3.7–5.8 apfu) shifting S from site S(2) by 0.42–0.44 Å.
Determined unit cell parameters for various argentotetrahedrite samples, revealing compression effects linked to increasing Ag content.
Showed that the sequence of Cu to Ag substitution in octahedral clusters affects the S atom's positioning.

Abstract

Using electron microprobe analysis and X-ray diffraction (XRD), we studied crystal fragments of four minerals of the fahlore group from the Mangazeyskoye Ag–Pb–Zn deposit (Yakutia, Russia) with 3. 7–5. 8 atoms per formula units (apfu) Ag and 13–12 apfu S. Both methods revealed a negative correlation between Ag and S contents in the fahlore chemical composition. The crystal structures of four Ag-bearing fahlores are refined using XRD. The parameters of their unit cells (a0, Å) in group I 43m (cubic) are as follows: 10. 58829 for argentotetrahedrite- (Fe) (Ag3. 68Cu2. 32) Σ6 (Cu4. 04Fe1. 73Zn0. 27Σ2. 00) Σ6. 04 (Sb3. 94As0. 03) Σ3. 97S12S1. 01; 10. 53378 for argentotetrahedrite- (Zn) (Ag3. 82Cu2. 18) Σ6 (Cu4. 09Zn1. 71Fe0. 28Σ1. 99) Σ6. 08 (Sb3. 82As0. 10) Σ3. 92S12. 74; 10. 51544 for kenoargentotetrahedrite- (Fe) (Ag4. 34Cu1. 66) Σ6 (Cu4. 10Zn0. 96Fe1. 03Σ1. 98) Σ6. 08 (Sb3. 88As0. 03) Σ3. 92S12. 47; and 10. 48411 for kenoargentotetrahedrite- (Zn) (Ag5. 83Cu0. 17) Σ6 (Cu3. 96Zn1. 98Fe0. 04Σ2. 02) Σ5. 98 (Sb3. 99As0. 02) Σ4. 01S12S0. 04. The XRD studies of the fahlore crystal structure with a high resolution (2θmax = 82°) allowed us to refine the positions of Ag and Cu atoms in site M (2) and to find for the first time a new sulfur site S (3). А high Ag content (3. 7–5. 8 apfu) shifts S from site S (2) in the center of the octahedron by 0. 42–0. 44 Å to site S (3), which is located on a 3m symmetry element. Quantum chemical modeling showed that the sequential substitution of Cu atoms by Ag atoms in octahedral cluster SCu64+ gradually shifts the S atom from the center of the octahedron that illustrates the transition from site S (2) in the pure Cu cluster to the refined site S (3) in cases of mixed clusters S (Ag, Cu) 6. The unit cell parameter depends on the size of the Ag, Cu6 octahedral cluster in the fahlore crystal structure, which is compressed with an increasing Ag content due to a decrease in the Ag1–Ag1, Cu1–S (3), and Ag1–S (3) distances.

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Cite This Study

Lyubimtseva et al. (Fri,) studied this question.

synapsesocial.com/papers/6a1fc56bdee9eb8c0dce6e7e https://doi.org/https://doi.org/10.1134/s1028334x26600465

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