Transmission electron microscopy investigation of Ag-free lillianite and heyrovskyite from Vulcano, Aeolian Islands, Italy

Researchers have identified the first evidence of incommensurate structural modulation in heyrovskýite (Pb6Bi2S9), a rare silver- and copper-free sulfosalt from Vulcano, Aeolian Islands. This unique modulation, characterized by an angle of ~29° relative to the b* axis and a wavelength of ~75 Å, suggests a possible ordering process of Pb and Bi cations or vacancies within the mineral's structure. While ion-milling during sample preparation may have induced this feature, its potential as a primary characteristic of heyrovskýite cannot be excluded. The study employed transmission electron microscopy (TEM), including selected area electron diffraction (SAED) and high-resolution TEM (HRTEM), to analyze specimens prepared via crushing, ion-milling, and ultramicrotomy, revealing well-ordered crystals with minor stacking faults and rare nanoscale intergrowths of lillianite and heyrovskýite.

Mitolo, D., Capitani, G. C., Garavelli, A., & Pinto, D. (2011). Transmission electron microscopy investigation of Ag-free lillianite and heyrovskyite from Vulcano, Aeolian Islands, Italy. American Mineralogist, 96(2-3), 288–300. https://doi.org/10.2138/am.2011.3530