The new mineral, heimaeyite, was found among the fumarolic encrustations collected on Eldfell volcano, on the island of Heimaey, Iceland. The mineral formed as microscopic rounded aggregates (<50 m) and rounded grains (<10 m) mixed with tiny needles of koryakite and a mineral phase with an NaMgAl(SO4)(3) composition. It was formed in scoria consisting of anhydrite, hematite, and cristobalite. Other associated minerals are tamarugite, hexahydrite, l & ouml;weite, and langbeinite. Heimaeyite is orange with a yellowish streak. It is translucent with a vitreous lustre. The calculated density is 2.783 g cm(-3). The chemical analysis gives a composition of Na2.93Al0.82Fe0.25S2.99O12.05. The ideal formula is Na3Al(SO4)(3) with 10 % to 25 % replacement of Al with Fe. Single-crystal X-ray diffraction analysis shows that it is trigonal and has a space group of with unit cell parameters of a=13.4326(9) & Aring;, c=8.9818(7) & Aring;, V=1403.5(2) & Aring;(3), and Z=6. The X-ray powder diffraction resembles that of Na3V(SO4)(3) (PDF 39-0243), with which it is isostructural. They both belong to the K7Nb(SO4)(6) structure type. In the crystal structure, the octahedral coordinations of the cation (in heimaeyite this is Al) are connected by sulfate tetrahedra in a "pin-wheel" arrangement into chains extending along [001]. The chains are interconnected by [NaO6] distorted trigonal prism coordinations. Fe substitutes for Al in the larger of the two symmetry-independent octahedral sites. Synthetic pure Na3Al(SO4)(3) was prepared through a solid-state reaction at 550 degrees C, and its structure was refined by the Rietveld method. It shows a smaller difference in size between the two octahedral sites than the natural sample.

Sant’Angelo in Criptis (Santeramo in Puglia, South Italy) is a karst cave located in the Alta Murgia National Park (aspiring geopark), presently degraded, but with signs of intense past visiting activity for worship, as testified by the beautiful wall paintings and the large number of inscriptions and engravings on the cave walls. With the aim to permit the desirable restoration and the following fruition of this ancient geo-cultural heritage, a multidisciplinary investigation of the cave was carried out in this study. The 3D cave model permitted a detailed map of the area and highlighted that the cave vault, although very regular, somewhere presents chimneys that develop upwards, indicating areas where the rock thickness is now very small. The stability analysis indicates that presently, the cave does not show remarkable signs of instability, but block failures, toppling and roof collapse are possible. Archaeometry investigations confirmed the past importance of this holy site, as testified by the overlapping in the paintings of three different pictorial cycles and the use of precious pigments, thus confirming the necessity of preservation through a conservation management strategy for a full future fruition of the cave.

The paper deals with the archaeometric investigation of wall paintings in the Sant'Angelo in Criptis karst cave in Santeramo in Colle (Southern Italy) dedicated to St. Michel the Archangel. The investigated wall paintings portray the Virgin with Child, the Christ Pantocrator and Descent of the Holy Spirit, both consisting of two overlapped pictorial cycles, and St. Michael the Archangel slaying the dragon, containing a single painting. Archaeometric research focuses on the characterisation of 56 samples of mortars and pictorial layers in terms of raw materials, pigment mixtures and painting techniques and aims to provide a meaningful contribute to the historical and chronological knowledge of the site. The analytical approach involved microstratigraphic observation under reflected-light optical microscope and compositional characterisation through micro-Raman spectroscopy and scanning electron microscope-energy dispersive X-ray spectroscopy. Results indicated a colour palette involving shades of red, yellow and black, obtained using common pigments such as red and yellow ochres and carbon black frequently mixed to each other, or with lime, to produce secondary hues and most precious pigment, as cinnabar. Mortar analysis provided information on technological aspects and helped to validate chronological hypotheses. The most relevant aspect emerging from results was the custom and the ability of the workers to mix few pigments to obtain several shades and chromatic nuances and the competence in the overlapping of different coloured layers to produce specific chromatic effects. Such considerations suggested the modus operandi of the artists who worked in the Apulia region in the Middle Ages and helped to define technical procedures and material features of the Apulian rupestrian paintings.

AbstractThermessaite-(NH4), ideally (NH4)2AlF3(SO4), is a new mineral found as a medium- to high-temperature (~250–300°C) fumarole encrustation at the rim of La Fossa crater, Vulcano, Aeolian Islands, Italy. The mineral deposited as aggregates of minute (<0.2 mm) sharp prismatic crystals on the surface of a pyroclastic breccia in association with thermessaite, sulfur, arcanite, mascagnite, and intermediate members of the arcanite–mascagnite series.The new mineral is colourless to white, transparent, non-fluorescent, has a vitreous lustre, and a white streak. The calculated density is 2.185 g/cm3. Thermessaite-(NH4) is orthorhombic, space group Pbcn, with a = 11.3005(3) Å, b = 8.6125(3) Å, c = 6.8501(2) Å, V = 666.69(4) Å3 and Z = 4. The eight strongest reflections in the powder X-ray diffraction data [d in Å (I)(hkl)] are: 5.65 (100)(200), 4.84 (89)(111), 6.85 (74)(110), 3.06 (56)(112), 3.06 (53)(221), 3.08 (47)(311), 2.68 (28)(022) and 2.78 (26)(130). The average chemical composition, determined by quantitative SEM-EDS (N by difference), is (wt.%): K2O 3.38, Al2O3 25.35, SO3 36.58, F 26.12, (NH4)2O 22.47, O = F –11.00, total 102.90. The empirical chemical formula, calculated on the basis of 7 anions per formula unit, is [(NH4)1.85K0.15]Σ2.00Al1.06F2.94S0.98O3.06. The crystal structure, determined from single-crystal X-ray diffraction data [R(F) = 0.0367], is characterised by corner-sharing AlF4O2 octahedra which form [001] octahedral chains by sharing two trans fluoride atoms [Al–F2 = 1.8394(6) Å]. Non-bridging Al–F1 distances are shorter [1.756(1) Å]. The two trans oxygen atoms [Al–O = 1.920(2) Å] are from SO4 tetrahedra. NH4+ ions occur in layers parallel to (100) which alternate regularly with (100) layers containing ribbons of corner-sharing AlF4O2 octahedra and associated SO4 groups. The NH4+ ions are surrounded by five oxygen atoms and by four fluorine atoms. The mineral is named as the (NH4)-analogue of thermessaite, K2AlF3(SO4), and corresponds to an anthropogenic phase found in the burning Anna I coal dump of the Anna mine, Aachen, Germany. Both mineral and mineral name have been approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA2011-077).

The new mineral topsoeite, FeF3(H2O)(3), was found as a fumarolic product after the 1991 eruption of Hekla, Iceland. The mineral occurs as up to 20 mu m large square-prismatic crystals forming occasional stepped aggregates or massive, up to 100 mu m wide veins, in association with several other fluorides, hematite and opal. The experimental formula of the mineral (from scanning electron microscope energy-dispersive spectrometry data) is Fe(F2.94Cl0.04)Sigma(2.98)(H2O)(1.94). The deficiency of water in the formula is most probably an artefact due to experimental limitations and not a sign of dehydration. The mineral is yellow, with a calculated density of 2.330 g.cm(-3), based on the ideal formula. It is tetragonal (P4/n) with a= 7.8381(3) angstrom, c= 3.8674(1) angstrom, V= 237.60(2)angstrom(3). The strongest eight powder diffraction lines are [d in angstrom (relative intensity) (hkl)]: 5.55 (100) (1 10); 3.92 (43) (0 2 0); 3.47 (39) (0 1 1); 3.17 (22) (11 1); 2.77 (30) (2 2 0); 2.479 (31) (1 3 0, 3 10); 1.877 (16) (0 1 2), 1.753 (24) (2 4 0, 4 2 0). Rietveld refinement of the powder diffraction data confirmed the identity of topsoeite with synthetic beta-FeF3(H2O)(3). The crystal structure consists of straight infinite chains of [FeF4(H2O)(2)] octahedra extending along the c axis. The adjacent octahedra share apical F atoms, whereas the four unshared, equatorially coordinated atoms are represented by a disordered arrangement of two F and two O atoms from water molecules. Additional water molecules occupy the spaces between chains and are tetrahedrally coordinated by four (F, H2O) from four different chains binding them together via hydrogen bonds. Topsoeite is isostructural with rosenbergite, AlF3(H2O)(3). Both minerals have rhombohedral polymorphs known from studies of phase systems. The polymorph of topsoeite (UM2008-27-F:AlHO), earlier supposed to be aluminium fluoride hydrate, was also found in Hekla fumaroles from the 1991 eruption, but its genetic relation with topsoeite remains unclear. Topsoeite is named after the family of Danish prominent scientists and industrialists including Haldor Topsoe the elder (1842-1935), Haldor Top sue the younger (1913-2013) and Henrik Topsoe (1944).

Verneite, Na2Ca3Al2F14, is a new mineral first discovered in fumarolic samples from both Hekla, Iceland and Vesuvius, Italy. Additional occurrences are so far from Eldfell and Fimmvörduhals, both on Iceland. Verneite is cubic, I213, a = 10.264(1) Å, V = 1081.4(3) Å3, Z = 4, and corresponds to the known synthetic compound. The empirical formula is Na2.01Ca2.82Al2.17F14.02 (scanning electron microscopy with energy dispersive spectrometer from an unpolished sample). It appears in crystals up to 20 μm in diameter, with {110}, {100}, and {111} as the main forms. In the crystal structure of its synthetic analogue, Na is coordinated by 7 F atoms in the form of a capped octahedron, Ca with 8 F atoms in the form of a bisdisphenoid, and Al with 6 F atoms in the form of an octahedron. The crystal structure of Na2Ca3Al2F14 contains sinuous chains of Ca coordination polyhedra interlacing with similarly sinuous chains of Na coordination polyhedra and forming together with them layers parallel to {100}. The intersecting layers parallel to three equivalent crystallographic planes form a three-dimensional mesh with Al coordinations imbedded in its holes. The characteristics of Ca coordinations in fluorides, as well as their relations to other ternary Na–Ca–Al fluorides are discussed. Verneite is named after Jules Verne.

The fumarolic mineralogy of the Icelandic active volcanoes, the Tyrrhenian volcanic belt (Italy) and the Aegean active arc (Greece) is investigated, and literature data surveyed in order to define the characteristics of the European fumarolic systems. They show broad diversity of mineral associations, with Vesuvius and Vulcano being also among the world localities richest in mineral species. Volcanic systems, which show recession over a longer period, show fumarolic development from the high-temperature alkaline halide/sulphate, calcic sulphate or sulphidic parageneses, synchronous with or immediately following the eruptions, through medium-temperature ammonium minerals, metal chlorides, or fluoride associations to the late low-temperature paragenesis dominated by sulphur, gypsum, alunogen, and other hydrous sulphates. The situation can be different in the systems that are not recessing but show fluctuations in activity, illustrated by the example of Vulcano where the high-temperature association appears intermittently. A full survey of the mineral groups and species is given in respect to their importance and appearance in fumarolic associations.

The crystal structure of baliczunicite, Bi2O(SO4)(2), a new mineral species from the La Fossa crater of Vulcano (Aeolian Islands, Italy), was solved from single-crystal X-ray diffraction data and refined to R = 0.0507. The structure is triclinic, space group P (1) over bar, with a = 6.7386(3), b = 11.1844(5), c = 14.1754(7) angstrom, alpha = 80.082(2), beta = 88.462(2)degrees, gamma = 89.517(2)degrees, V = 1052.01(8) angstrom(3) and Z = 6. The crystal structure consists of six independent Bi sites, six S sites and 27 O sites of which three are oxo oxygen atoms not bonded to sulfur. Bismuth and S atoms are arranged close to a eutectic pattern parallel to the (100) plane. The planes are stacked atom on atom such that Bi always overlays S and vice versa. This structural feature is shared with the known structure of the high-temperature polymorph of the same compound, stable at T > 535 degrees C. However, the sequences of Bi and S atoms in the two structures are different and so are the arrangements of oxygen atoms. Characteristic building blocks in the structure of baliczunicite are clusters of five Bi atoms which form nearly planar trapezoidal Bi-5 groups with oxo oxygens located in the centres of the three Bi-3 triangles, which form the trapezoids. The trapezoidal Bi5O39+ ions are joined along [100] with SO42- groups by means of strong bismuth-sulfate oxygen bonds, forming infinite [100] rods with composition Bi5O3(SO4)(5)(-). One sixth of the Bi atoms do not participate in trapezoids, but form, with additional SO42- groups, rows of composition BiSO4+, also parallel to [100]. [Bi5O3(SO4)(5)(-)] rods form infinite layers parallel to (010) with [BiSO4+] rows located on the irregular surface of contact between adjacent layers. Bi atoms occur in four different coordination types, all showing the stereochemical influence of the Bi3+ lone electron pair. In this respect the crystal structure of baliczunicite shows greater variability than its high-temperature polymorph which has only two types of the Bi coordination spheres present in baliczunicite.

The crystal structures of two new natural Bi oxysulfates with the formula Bi14O16(SO4)5 [labelled new phase I; monoclinic, space group C2, a = 21.658 (4), b = 5.6648 (9), c = 15.092 (3) Å, β = 119.433 (11)° and Z = 2] and Bi30O33(SO4)9(AsO4)2 [labelled new phase II; triclinic, space group P1, a = 5.670 (3), b = 13.9408 (9), c = 22.7908 (18) Å, α = 80.903 (5), β = 82.854 (14), γ = 78.27 (2)° and Z = 1] from the high-temperature fumarole deposit of the La Fossa crater at Vulcano (Aeolian Islands, Italy) are reported. The structures are built up by a combination of fluorite-related Bi-O units and isolated (SO4)(2-) tetrahedra (new phase I) or both (SO4)(2-) and (AsO4)(3-) tetrahedra (new phase II). Owing to the effect of stereoactive lone pairs of Bi(3+), Bi-O units in both the structures can be suitably described in terms of oxo-centered OBi4 tetrahedra. The structure of Bi14O16(SO4)5 is based upon one-dimensional [O16Bi14](10+) ribbons formed by six chains of edge-sharing OBi4 tetrahedra extending along [010]. In the structure of Bi30O33(SO4)9(AsO4)2 the same ribbon type coexists with another one-dimensional ribbon formed by seven chains of edge-sharing OBi4 tetrahedra and with the composition [O17Bi16](14+). Ribbons of the same type are joined by (SO4)(2-) and (AsO4)(3-) tetrahedra along [010] – if a reduced triclinic unit-cell setting is considered – so forming two different (001) slabs which alternate to each other along [001] and are joined by additional (SO4)(2-) tetrahedra. New phase I represents the natural analogues of synthetic Bi14O16(SO4)5, but with an ordered structure model.

Baliczunicite, ideally Bi2O(SO4)(2), is a new mineral found as a high-temperature fumarole sublimate (T = 600 degrees C) at La Fossa crater, Vulcano, Aeolian Islands, Italy. It occurs as aggregates of mu m-sized prismatic and elongated crystals (similar to 50 mu m across and up to 200 mu m long) associated with anglesite, leguernite, one other potentially new Bi-oxysulfate mineral, lillianite, galenobismutite, bismoclite, Cd-rich sphalerite, wurtzite, pyrite and pyrrhotite. Baliczunicite 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/cm(3).Baliczunicite is triclinic, space group P (1) over bar, with a 6.7386(3), b 11.1844(5), c 14.1754(7) angstrom, alpha 80.082(2)degrees, beta 88.462(2)degrees, gamma 89.517(2)degrees, V = 1052.01(8) angstrom(3) and Z = 6. The six strongest reflections in the X-ray powder-diffraction data [d in angstrom (I) (hkl)] are: 3.146 (100) (033), 3.486 (21) (004), 3.409 (12) (0 (3) over bar1), 3.366 (7) (200), 5.562 (4) (111), 5.433 (4) ((1) over bar 11). Baliczunicite is the natural analogue of the stable low-temperature alpha form of synthetic Bi2O(SO4)(2). The name is in honour of Tonci Balic-Zunic (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).

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 degrees 25'58.9''N 20 degrees 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 electron-microscope 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 R (3) over barc, with a(h) = 4.9817(4) angstrom, c = 12.387(1) angstrom, V-uc = 266.23(5) angstrom(3), Z = 6. The five strongest lines in the powder diffraction diagram [d in angstrom (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 perovskite-type 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.

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).

Lucabindiite, ideally (K,NH4)As4O6(Cl,Br), is a new mineral found as a medium-temperature fumarole encrustation (T = 170 degrees 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/cm(3). Lucabindiite is hexagonal, space group P6/mmm, with a = 5.2386(7) angstrom, c = 9.014(2) angstrom, V = 214.23(7) angstrom(3), and Z = 1. The eight strongest reflections in the X-ray powder-diffraction data [din angstrom (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)(2)O 2.73, O=F,Cl,Br -1.84, total 102.06. The empirical chemical formula, calculated on the basis of 7 anions pfu, is [K-0.51(NH4)(0.49)](Sigma 1.00) As4.00O5.93(Cl0.48Br0.40F0.19)(Sigma 1.07). 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).

Leonardsenite (IMA2011-059), with ideal formula MgAlF5(H2O)(2), is a new fumarole mineral from Eldfell volcano, Iceland. It has also been found in volcanic encrustations from the Hekla crater, Iceland. The mineral forms a soft and friable mass of white crystals up to 20 mu m in length. The streak is white and the luster is earthy. The calculated density is 2.31 g cm(-3). Leonardsenite is orthorhombic, space group Imma; the lattice parameters, obtained from Rietveld refinement of the XRPD data, are: a 7.055(1) A, b 10.117(2) angstrom, c 6.813(1) angstrom, V 486.3(1) angstrom(3), and Z = 4. The eight strongest reflections in the X-ray powder diffraction pattern are [d in A (I) (hkl)]: 5.66 (100) (011), 4.92 (29) (101), 3.53 (27) (200), 3.03 (31) (031), 3.00 (38) (211), 2.30 (16) (231), 1.77 (19) (400), 1.76 (24) (242). Chemical analyses by energy-dispersive spectrometry using a scanning electron microscope produced a mean elemental composition as follows (wt.%): Mg 14.66, Al 16.16, F 52.98, 0 15.88, H 1.78, total 101.46. The corresponding empirical formula, calculated on the basis of 2 cations pfu, is Mgi.00Ali 004.64(011)0.361E5.00(1420)1 29. On the basis of chemical analyses and X-ray diffraction data, leonardsenite corresponds to the synthetic compound MgAlF5(H2O)(2). The crystal structure of leonardsenite contains infinite chains of [A(1)F(6)] octahedra along the c-axis which are connected via common fluorine atoms to isolated [MgF4(H2O)(2)] octahedra. Leonardsenite is the first aluminum fluoride hydrated mineral of the inverse weberite group with general formula (MMTIF5)-M-II-T-I(H2O)(2). Leonardsenite belongs to the group of fluorides with interesting optical and catalytic properties. The name of this new species honors Erik Leonardsen (1934), the former leader of the X-Ray Diffraction Laboratory of the Geological Institute, University of Copenhagen. The mineral and its name have been approved by the MA-CNMNC (IMA2011-059).

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 mu m 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)(Sigma 0.84)Al1.06F4.09(OH)(1.01). Jakobssonite is monoclinic, space group C2/c, with a = 8.601(1), b = 6.2903(6), c = 7.2190(7) angstrom, beta = 114.61(1)degrees, V = 355.09(8) angstrom(3) 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 (CaMF5)-F-III compounds. The eight strongest lines in the powder diffraction diagram [d in angstrom (I) (hkl)] are as follows: 4.91 (18) (110), 3.92 (76) (200), 3.15 (68) (020), 3.13 (100) (1<(1)over bar>(2) over bar), 2.27 (22) (2 (2) over bar(2) over bar), 1.957 (21) (400), 1.814 (20) (1 (3) over bar(2) over bar), 1.805 (22) (20 (4) over bar). 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.

We present a transmission electron microscopy (TEM) investigation of lillianite (Pb(3)Bi(2)S(6)) and heyrovskyite (Pb(6)Bi(2)S(9)), 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 well-ordered crystals with only minor stacking faults and, more rarely, nanoscale intergrowths of lillianite and heyrovskyite. The latter were sometimes found to form an incommensurate structural modulation with an angle of similar to 29 degrees relative to b* in the (hk0) plane and a wavelength of similar to 75 angstrom. This represents the first observation of such incommensurate modulations in heyrovskyite. 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 heyrovskyite 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 Bi(2)S(3) sublimation during ion-milling.