ADRANOSITE, (NH4)4NaAl2(SO4)4Cl(OH)2, A NEW AMMONIUM SULFATE CHLORIDE FROM LA FOSSA CRATER, VULCANO, AEOLIAN ISLANDS, ITALY

The new mineral species adranosite, (NH4)4NaAl2(SO4)4Cl(OH)2, was found in a medium-temperature (~250°C) active fumarole at La Fossa crater, Vulcano, Aeolian Islands, Sicily, Italy. The mineral occurs on a pyroclastic breccia as colorless to white sprays of prismatic crystals up to 0.3 mm in length, in association with aiolosite, alunite, anhydrite, bismuthinite, sassolite, demicheleite-(Br), demicheleite-(Cl), panichiite and IMA 2009–049. The mineral is tetragonal, space group: I41/acd (no. 142) with a 18.118(3), c 11.320(3) Å, V 3715.5(13) Å3 and Z = 8. The strongest six reflections in the X-ray powder-diffraction pattern [dobs in Å(I)(hkl)] are: 2.980(100)(152), 2.265(87)(080), 4.530(86)(040), 6.398(80)(220), 3.020(65)(060) and 3.202(47)(440). The average result of chemical analyses (wt.%) is: Na2O 5.88, Al2O3 17.40, K2O 0.90, (NH4)2O 16.52, SO3 51.31, Cl 5.68, H2O 2.99, –O=Cl –1.28, for a total of 99.40. The empirical formula (based on 19 anions) is: [(NH4)3.89K0.12]S4.01Na1.16Al2.09S3.93O15.99 Cl0.98(OH)2.03. The end-member formula is (NH4)4NaAl2(SO4)4Cl(OH)2. The measured density is 2.15(1) g/cm3, and Dcalc is 2.176 g cm–3. The mineral is uniaxial (–) with v = 1.55(1),  = 1.54(1) (l = 589 nm). Using single-crystal diffraction data, the structure was refined to a final R = 0.0355 for 596 independent observed reflections [I > 2s(I)]. Adranosite is isostructural with the (NH4)4NaFe2(SO4)4Cl(OH)2 phase found in a burning coal dump. Building blocks of the structure are AlO6 octahedra [Al–O in the range 1.862(1)–1.923(1) Å] and SO4 tetrahedra, which are linked together to form spiraling chains parallel to [001]. There are also NaO4Cl2 square tetragonal bipyramids [Na–O 2.360(1), Na–Cl 2.830(1) Å], linked together by sharing the Cl atoms at the corners. The ammonium ions occupy the voids in the resulting framework and interact with the neighboring atoms via hydrogen bonds.