Structure refinement of Ag-free heyrovskyite from Vulcano (Aeolian Islands, Italy)

Researchers have identified the first single-crystal structure refinement of silver (Ag)- and copper (Cu)-free heyrovskýite, a rare mineral found in the high-temperature fumaroles of La Fossa crater on Vulcano Island, part of Italy's Aeolian Islands. The study reveals that heyrovskýite deviates slightly from its ideal composition (Pb6Bi2S9) due to vacancies and selenium substitutions, with lead (Pb) predominantly occupying specific sites while bismuth (Bi) is mixed in others. This finding supports a structural model suggesting that heyrovskýite exists as a fully disordered polymorph of Pb6Bi2S9, contrasting with its ordered monoclinic counterpart, aschamalmite. The study also notes that Ag incorporation increases disorder and stabilizes the orthorhombic form of heyrovskýite.

Pinto, D., Balic-Zunic, T., Garavelli, A., & Vurro, F. (2011). Structure refinement of Ag-free heyrovskyite from Vulcano (Aeolian Islands, Italy). American Mineralogist, 96(7), 1120–1128. https://doi.org/10.2138/am.2011.3635