ALBERT

Description: The new mineral adranosite-(Fe), ideally (NH 4 ) 4 NaFe 2 (SO 4 ) 4 Cl(OH) 2 , is the Fe 3+ -analogue of adranosite. It was found on a pyroclastic breccia in two different fumaroles at "La Fossa" crater of Vulcano, Aeolian Islands, Italy, and corresponds to an anthropogenic product previously observed in a burning coal dump at the Anna mine, near Aachen, Germany. The mineral is tetragonal, space group I 4 1 / acd (no. 142), with a = 18.261(2), c = 11.562(1) Å, V = 3855.5(7) Å 3 (single-crystal data), and Z = 8. The six strongest reflections in the X-ray powder diffraction pattern are [ d obs in Å ( I )( hkl )]: 9.134(100)(020), 4.569(83)(040), 3.047(79)(152), 6.462(36)(220), 3.232(29)(251), and 2.891(11)(004). The average chemical composition of the holotype is (wt.%): Na 2 O 5.01, Fe 2 O 3 15.77, Al 2 O 3 5.11, K 2 O 0.82, (NH 4 ) 2 O 15.76, SO 3 50.96, Cl 3.71, H 2 O 2.75, –O=Cl–0.84, total 99.05; the corresponding empirical formula is: [(NH 4 ) 3.89 K 0.11 ] 4.00 Na 1.04 [Fe 1.27 Al 0.64 ] 1.91 S 4.10 O 16.40 C l0.67 (OH) 1.96 . Adranosite-(Fe) forms aggregates of pale yellow acicular crystals up to 1 mm in length, the most common forms most probably being {100}, {110}, and {111}. The measured density is 2.18(1) g/cm 3 , and the calculated density is 2.195 g/cm 3 . Adranosite-(Fe) is uniaxial (–) with =1.58(1), =1.57(1) ( = 589 nm). Using single-crystal X-ray diffraction data from the holotype, the structure was refined to a final R ( F )= 0.0415 for 670 independent observed reflections [ I 〉 2(( I )]. Adranosite-(Fe) is isostructural with its Al-analogue adranosite and contains NaO 4 Cl 2 square tetragonal bipyramids, linked through their opposite Cl corners and helicoidal chains with composition [FeO 4 (OH) 2 SO 4 ] n , both extending along [001]. The framework resulting from the sharing of the sulfate ions between the different chains displays cages in which the nine-coordinated hydrogen-bonded NH 4 + ions are hosted.