2013/06/01 by Francesco Demartin, Carlo Castellano, I. Campostrini · 4 citations
Materials Science · Environmental Science · #Crystal Structures and Properties #X-ray Diffraction in Crystallography #Chemical Synthesis and Characterization
paper · doi:10.1180/minmag.2013.077.4.04
openalex publication_date 2013/06/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/11
Abstract The new mineral aluminopyracmonite, ideally (NH 4 ) 3 Al(SO 4 ) 3 , was found in a medium-temperature (∼250°C) intracrater active fumarole at La Fossa crater, Vulcano, Aeolian Islands, Sicily, Italy. It occurs on a pyroclastic breccia as colourless to white prismatic crystals up to 0.2 mm long, in association with adranosite, mascagnite, alunite and salammoniac. The mineral is identical to the synthetic compound (NH 4 ) 3 Al(SO 4 ) 3 . It is trigonal, space group: R (no. 148) with a = 15.0324(8), c = 8.8776(5) 5, V = 1737.3(2) Å 3 and Z = 6. The six strongest reflections in the X-ray powder diffraction pattern are: [ d obs in Å (I)(hkl) ] 3.336(100)(131), 7.469(62)(1 1 0), 3.288(60)(122), 4.289(45)( 31), 2.824(29)( 51), 4.187(27) (012). The empirical formula based on 12 anions is [(NH 4 ) 2.89 K 0.10 ] Σ 2.99 (Al 1.18 Fe 0.01 ) Σ 1.19 S 2.91 O 12 , and the simplified formula (NH 4 ,K) 3 Al(SO 4 ) 3 . The measured density is 2.12(1) g/cm 3 , calculated density 2.143 g/cm 3 . The mineral is uniaxial(–) with ω = 1.545(3) and ε = 1.532(3) (λ = 589 nm). Using single-crystal diffraction data, the structure was refined to a final R(F) = 0.0258 for 998 independent observed reflections [ I > 2σ( I )]. In spite of having unitcell parameters comparable with those of pyracmonite, the two minerals are not isostructural; the difference is related to a disordered conformation of the sulfate anions about the two independent Al 3+ ions in aluminopyracmonite.