Demicheleite-(I), BiSI, a new mineral from La Fossa Crater, Vulcano, Aeolian Islands, Italy

Researchers have discovered demicheleite-(I), BiSI, a new bismuth sulphoiodide mineral, in the active fumaroles of La Fossa Crater on Vulcano Island, part of the UNESCO-listed Aeolian Islands. This is the first naturally occurring bismuth sulphoiodide identified, matching a previously synthesized compound. The mineral appears as dark red to black, acicular crystals up to 0.25 mm long, found alongside other phases like demicheleite-(Br), bismoclite, and bismuthinite. Its orthorhombic crystal structure (space group Pnam) was determined using X-ray diffraction, with a calculated density of 6.411 g/cm³. Chemical analysis revealed an empirical formula close to Bi0.97S1.03(I0.65Br0.25Cl0.10). The discovery highlights the unique mineralogical diversity of volcanic environments and expands the known range of bismuth-based minerals.

Demartin, F., Gramaccioli, C. M., & Campostrini, I. (2010). Demicheleite-(I), BiSI, a new mineral from La Fossa Crater, Vulcano, Aeolian Islands, Italy. Mineralogical Magazine, 74(1), 141–145. https://doi.org/10.1180/minmag.2010.074.1.141