Pyrachmonite, (NH4)3Fe(SO4)3, a New Ammonium Iron Sulfate from La Fossa Crater, Vulcano, Aeolian Islands, Italy

Scientists have identified pyracmonite, (NH4)3Fe(SO4)3, a new ammonium iron sulfate mineral, within the active intracrater fumarole of La Fossa crater on Vulcano Island in Italy's Aeolian Islands. This discovery, occurring at approximately 250°C, reveals its trigonal crystal structure and association with other minerals like salammoniac and kremersite. Pyracmonite exhibits unique properties such as a measured density of 2.22(1) g/cm³, an average refractive index of 1.562(3), and a structure identical to synthetic (NH4)3Fe(SO4)3, indicating its significance in mineralogy. The study utilized single-crystal X-ray diffraction, confirming the mineral's isostructural relationship with high-temperature synthetic compounds, thereby advancing our understanding of volcanic minerals.

Demartin, F., Gramaccioli, C. M., & Campostrini, I. (2010). PYRACMONITE, (NH4)3Fe(SO4)3, A NEW AMMONIUM IRON SULFATE FROM LA FOSSA CRATER, VULCANO, AEOLIAN ISLANDS, ITALY. The Canadian Mineralogist, 48(2), 307–313. https://doi.org/10.3749/canmin.48.2.307