Donatella Mitolo

Lucabindiite, (K,NH4)As4O6(Cl,Br), a new fumarole mineral from the “La Fossa” crater at Vulcano, Aeolian Islands, Italy

Abstract Lucabindiite, ideally (K,NH4)As4O6(Cl,Br), is a new mineral found as a medium-temperature fumarole encrustation (T = 170 °C) at “La Fossa” crater of Vulcano, Aeolian Islands, Italy. The mineral deposited as aggregates of micrometer-sized hexagonal and platy crystals on the surface of the pyroclastic breccia in association with arsenolite, sal ammoniac, sulfur, and amorphous arsenic-rich sulfurite. The new mineral is colorless to white, transparent, non-fluorescent, has a vitreous luster and a white streak. The calculated density is 3.68 g/cm3. Lucabindiite is hexagonal, space group P6/mmm, with a = 5.2386(7) Å, c = 9.014(2) Å, V = 214.23(7) Å3, and Z = 1. The eight strongest reflections in the X-ray powderdiffraction data [d in Å (I) (hkl)] are: 3.20 (100) (102), 2.62 (67) (110), 4.51 (52) (002), 4.54 (30) (100), 1.97 (28) (113), 1.49 (21) (115), 1.60 (21) (212), 2.26 (19) (112). Lucabindiite’s average chemical composition is (wt%): K2O 5.14, As2O3 84.71, Cl 3.63, Br 6.92, F 0.77, (NH4)2O 2.73, O=F,Cl,Br -1.84, total 102.06. The empirical chemical formula, calculated on the basis of 7 anions pfu, is [K0.51(NH4)0.49]Σ1.00 As4.00O5.93(Cl0.48Br0.40F0.19)Σ1.07. According to chemical analyses and X-ray data, lucabindiite is the natural analog of synthetic phases with general formula MAs4O6X where M = K, NH4 and X = Cl, Br, I. The crystal structure is characterized by neutral As2O3 sheets arranged parallel to (001). The As atoms of two neighboring sheets point at each other and the sheets are separated by interlayer M (=K, NH4) and X (=Cl, Br, F) atoms. The name is in honor of Luca Bindi (b. 1971), Professor of Mineralogy and former Head of the Division of Mineralogy of the Natural History Museum of the University of Florence. Both the mineral and the mineral name have been approved by the IMA-CNMNC Commission (IMA 2011-010).

Balićžunićite, Bi2O(SO4)2, a new fumarole mineral from La Fossa crater, Vulcano, Aeolian Islands, Italy

Abstract Balićžunićite, ideally Bi2O(SO4)2, is a new mineral found as a high-temperature fumarole sublimate (T = 600°C) at La Fossa crater, Vulcano, Aeolian Islands, Italy. It occurs as aggregates of mm-sized prismatic and elongated crystals (~50 mm across and up to 200 mm long) associated with anglesite, leguernite, one other potentially new Bi-oxysulfate mineral, lillianite, galenobismutite, bismoclite, Cd-rich sphalerite, wurtzite, pyrite and pyrrhotite. Balićžunićite is colourless to white or pale brown, transparent and non-fluorescent. It has a vitreous lustre and a white streak. Electron microprobe analysis gives the following average chemical composition (wt.%): Bi2O3 68.68 and SO3 23.73, total 92.41. The empirical chemical formula, calculated on the basis of 9 anions p.f.u., is Bi1.99S2O9. The calculated density is 5.911 g/cm3. Balićžunićite is triclinic, space group P1̅, with a 6.7386(3), b 11.1844(5), c 14.1754(7) Å , a 80.082(2)°, b 88.462(2)°, g 89.517(2)°, V = 1052.01(8) Å3 and Z = 6. The six strongest reflections in the X-ray powder-diffraction data [d in Å (I) (hkl)] are: 3.146 (100) (033), 3.486 (21) (004), 3.409 (12) (03̅1), 3.366 (7) (200), 5.562 (4) (111), 5.433 (4) (1̅11). Balićžunićite is the natural analogue of the stable low-temperature a form of synthetic Bi2O(SO4)2. The name is in honour of Tonci Balić-Žunić (born 1952), Professor of Mineralogy at the Natural History Museum of the University of Cophenagen. Both the mineral and the mineral name have been approved by the IMA-CNMNC Commission (IMA2012-098).

Leguernite, Bi12.67O14(SO4)5, a new Bi oxysulfate from the fumarole deposit of La Fossa crater, Vulcano, Aeolian Islands, Italy

Abstract Leguernite, ideally Bi12.67O14(SO4)5, is a new mineral found in high-temperature fumarolic assemblages at La Fossa crater, Vulcano, Aeolian Islands, Italy. It occurs as aggregates of needleshaped crystals associated strictly with anglesite, bali ćžunićite and an unknown Bi sulfate. Leguernite is colourless to white, transparent, non-fluorescent, has a sub-adamantine lustre and a white streak. Electron microprobe data led to the chemical formula (on the basis of 34 anions p.f.u.) (Bi12.40Pb0.15)∑=12.55S5.08O34. The calculated density is 7.375 g cm-3. A Raman spectrum collected on a single crystal of leguernite confirmed the anhydrous nature of the mineral. Leguernite is monoclinic, space group P2, with a = 11.2486(11), b = 5.6568(6), c = 11.9139(10) Å , β = 99.177(7)°, V = 748.39(12) Å3 and Z = 1. The crystal structure is built up of Bi-O blocks of a fluorite-like structure with Bi12O14 composition separated by a single sulfate ion along [100] and by Bi(SO4)45- groups along [101]. It can also be described as composed of (001) layers with composition [Bi12O14(SO4)6+]n alternating with layers of composition [Bi(SO4)4]n5- along [001]. Leguernite shows significant similarities with the synthetic Bi14O16(SO4)5 compound. The eight strongest reflections in the powder X-ray diffraction data [d in Å (I) (hkl)] are: 3.220 (100) (013), 3.100 (95) (3̄11), 2.83 (30) (020), 2.931 (25) (302), 2.502 (25) (3̄ 04), 2.035 (20) (322), 1.875 (20) (3̄24) and 5.040 (15) (110). The name is in honour of François ‘‘Fanfan’’ Le Guern (1942-2011), who was a very active volcanologist and specialist in volcanic gases and sublimates. Both the mineral and the mineral name have been approved by the IMA-CNMNC (2013-051).

Heklaite, KNaSiF6, a new fumarolic mineral from Hekla volcano, Iceland

Abstract Heklaite, with the ideal formula KNaSiF6, was found among fumarolic encrustations collected in 1992 on the Hekla volcano, Iceland. Heklaite forms a fine-grained mass of micron- to sub-micron-sized crystals intimately associated with malladrite, hieratite and ralstonite. The mineral is colourless, transparent, non-fluorescent, has a vitreous lustre and a white streak. The calculated density is 2.69 g cm-3. An SEM-EDS quantitative chemical analysis shows the following range of concentrations (wt.%): Na 11.61-12.74 (average 11.98), K 17.02-18.97 (average 18.29), Si 13.48-14.17 (average 13.91), F 54.88-56.19 (average 55.66). The empirical chemical formula, calculated on the basis of 9 a.p.f.u., is Na1.07K0.96Si1.01F5.97. X-ray powder diffraction indicates that heklaite is orthorhombic, space group Pnma, with the following unit-cell parameters: a = 9.3387(7) Å, b = 5.5032(4) Å, c = 9.7957(8) Å, V = 503.43(7) Å3, Z = 4. The eight strongest reflections in the powder diffraction pattern [d in Å (I/I0) (hkl)] are: 4.33 (53) (102); 4.26 (56) (111); 3.40 (49) (112); 3.37 (47) (202); 3.34 (100) (211); 2.251 (27) (303); 2.050 (52) (123); 2.016 (29) (321). On the basis of chemical analyses and X-ray data, heklaite corresponds to the synthetic compound KNaSiF6. The name is for the type locality, the Hekla volcano, Iceland.

Transmission electron microscopy investigation of Ag-free lillianite and heyrovskýite from Vulcano, Aeolian Islands, Italy

Abstract We present a transmission electron microscopy (TEM) investigation of lillianite (Pb3Bi2S6) and heyrovskýite (Pb6Bi2S9), from Vulcano, Aeolian Islands, Italy. The minerals investigated represent the only naturally occurring Ag- and Cu-free sulfosalts in the lillianite homologous series (LHS). Three methods (crushing, ion-milling, and ultramicrotomy) were used to prepare TEM specimens. Selected area electron diffraction (SAED) patterns and high-resolution TEM (HRTEM) images indicate wellordered crystals with only minor stacking faults and, more rarely, nanoscale intergrowths of lillianite and heyrovskýite. The latter were sometimes found to form an incommensurate structural modulation with an angle of ~29° relative to b* in the (hk0) plane and a wavelength of ~75 Å. This represents the first observation of such incommensurate modulations in heyrovskýite. Although considerable evidence points toward an artifact induced by the sample preparation technique (i.e., ion-milling), the possibility that the incommensurate modulation could be a primary feature of heyrovskýite itself cannot be completely ruled out. The modulation could derive from an ordering process of Pb and Bi cations over Me4 and Me5 sites within the PbS-like layer or from ordering of vacancies, naturally present or induced by Bi2S3 sublimation during ion-milling

Jakobssonite, CaAlF5, a new mineral from fumaroles at the Eldfell and Hekla volcanoes, Iceland

Abstract The new mineral jakobssonite, ideally CaAlF5, was first found in crusts collected in 1988 from a fumarole on the Eldfell volcano, Heimaey Island, Iceland. It was subsequently found in similar crusts collected in 1991 from a fumarole on the Hekla volcano, Iceland. It is associated with leonardsenite (IMA2011-059), ralstonite, heklaite, anhydrite, gypsum, jarosite, hematite, opal and several fluoride minerals that have not been fully characterized. Jakobssonite occurs as soft white fragile crusts of acicular crystals <50 μm long. Its calculated density is 2.89 g cm-3. Chemical analyses by energy-dispersive spectrometry on a scanning electron microscope produced a mean elemental composition as follows: Ca, 18.99; Al, 18.55; Mg, 1.33; Na, 0.33; F, 50.20; O, 10.39; total 99.79 wt.%. The empirical chemical formula, calculated on the basis of 7 atoms per formula unit with all of the oxygen as OH, is (Ca0.73Mg0.09Na0.02)S 0.84Al1.06F4.09(OH)1.01. Jakobssonite is monoclinic, space group C2/c, with a = 8.601(1), b = 6.2903(6), c = 7.2190(7) Å, β = 114.61(1)o, V = 355.09(8) Å3 and Z = 4. The crystal structure contains chains of [AlF6] octahedra which run parallel to the c axis. These chains are interconnected by chains of [CaF7] pentagonal bipyramids. Jakobssonite is isostructural with several other CaMIII F5 compounds. The eight strongest lines in the powder diffraction diagram [d in Å (I) (hkl)] are as follows: 4.91 (18) (110), 3.92 (76) (200), 3.15 (68) (020), 3.13 (100) (11̅2̅), 2.27 (22) (22̅2̅), 1.957 (21) (400), 1.814 (20) (13̅2̅), 1.805 (22) (204̅). The chemical and crystal-structure analyses of jakobssonite are similar to synthetic CaAlF5 with minor substitutions of light elements (e.g. Na) or vacancies for Ca, and OH for F.

Oskarssonite, AlF3, a new fumarolic mineral from Eldfell volcano, Heimaey, Iceland

Abstract The new mineral oskarssonite (IMA2012-088), with ideal formula AlF3, was found in August 2009 at the surface of fumaroles on the Eldfell volcano, Heimaey Island, Iceland (GPS coordinates 63°25′58.9″N 20°14′50.3″W). It occurs as sub-micron-sized crystals forming a white powder in association with anhydrite, bassanite, gypsum, jarosite, anatase, hematite, opal, ralstonite, jakobssonite and meniaylovite. Chemical analyses by energy-dispersive spectrometry with a scanning electronmicroscope produced the following mean elemental composition: Al, 31.70; F, 58.41; O, 9.22; total 99.33 wt.%. The empirical chemical formula is AlF2.6(OH)0.5 which suggests partial substitution of F by OH. Oskarssonite is rhombohedral, space group R3̄c, with ah = 4.9817(4) Å , c = 12.387(1) Å , Vuc = 266.23(5) Å3, Z = 6. The five strongest lines in the powder diffraction diagram [d in Å (I) (hkl)] are as follows: 3.54 (100) (012), 2.131 (13) (113), 1.771 (20) (024), 1.59 (15) (116), 1.574 (10) (122). Rietveld refinement confirms the identity of oskarssonite with the synthetic rhombohedral form of AlF3. Its structure can be described as a rhombohedral deformation of the idealized cubic perovskitetype octahedral framework of corner-sharing AlF6 groups. Oskarssonite appears in the surface part of the fumaroles where fluorides are abundant. At greater depths (below 10 cm) sulfates dominate among the fumarolic minerals. In accordance with its occurrence, we surmise that oskarssonite forms in the later stages of the fumarolic activity in an environment poor in alkalies and Mg. Ralstonite (NaxMgxAl1-xF3(H2O)y), which, unlike oskarssonite, contains Na and Mg as important constituents, dominated in the first-formed fumaroles, but now, 41 years after the eruption of Eldfell, is only a minor phase. The new mineral is named after the Icelandic volcanologist Niels Oskarsson.