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Mineralogy, crystal chemistry and structures of sulfosalts from Vulcano (Aeolian islands, Italy): Ag-free lillianite, Cl-bearing galenobismutite, kirkiite and the new mineral vurroite
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Oxo-centered structural units in bismuth oxysulfates from Vulcano, Aeolian Islands, Italy
No full textThe crystal structure of balićžunićite, Bi2O(SO4)2, a new natural bismuth oxide sulphate
No full textThe crystal structure of balićžunićite, Bi2O(SO4)2, a new mineral species from "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, with lattice parameters a 6.7386(3), b 11.1844(5), c 14.1754(7) Å, α 80.082(2){degree sign}, β 88.462(2){degree sign}, γ 89.517(2){degree sign}, V 1052.01(8) Å3 and Z = 6. The crystal structure consists of 6 independent Bi sites, 6 S sites and 27 O sites of which 3 are oxo oxygen atoms not bonded to sulphur. Bi and S atoms are arranged close to an eutectic pattern parallel to the (100) crystal planes. 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 over 535oC. 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 balićžunićite are clusters of five Bi atoms which form nearly planar trapezoidal Bi5 groups with oxo oxygens located in the centres of the three Bi3 triangles which form the trapezoids. The trapezoidal Bi5O39+ ions are joined along [100] with SO42- groups by means of strong bismuth-sulphate oxygen bonds, forming infinite [100] rods with composition Bi5O3(SO4)51-. One sixths of Bi atoms do not participate in trapezoids, but form with additional SO42- groups rows of composition BiSO41+, also parallel to [100]. [Bi5O3(SO4)51-] rods form infinite layers parallel to the crystal plane (010) with [BiSO41+] 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 balićžunićite shows greater variability than its high temperature polymorph which has only two types of Bi coordinations present in balićžunićite
Balićžunićite, Bi2O(SO4)2, a new fumarole mineral from la Fossa crater, Vulcano, Aeolian Islands, Italy
No full textBalic ́zˇunic ́ite, ideally Bi2O(SO4)2, is a new mineral found as a high-temperature fumarole sublimate
(T = 600oC) 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. Balic ́zˇunic ́ite is colourless to white or pale brown,
transparent, non-fluorescent. It has a vitreous lustre and a white streak. Electron microprobe analyses
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.
Balic ́zˇunic ́ite is triclinic, space group P1 ̄ , with a 6.7386(3), b 11.1844(5), c 14.1754(7) A ̊ ,
a 80.082(2)o, b 88.462(2)o, g 89.517(2)o, V = 1052.01(8) A ̊ 3 and Z = 6. The six strongest reflections in
the X-ray powder-diffraction data [d in A ̊ (I) (hkl)] are: 3.146 (100) (033), 3.486 (21) (004), 3.409 (12)
(03 ̄ 1), 3.366 (7) (200), 5.562 (4) (111), 5.433 (4) (1 ̄11). Balic ́zˇunic ́ite is the natural analogue of the
stable low-temperature a form of synthetic Bi2O(SO4)2. The name is in honour of Tonci Balic ́-Zˇ unic ́
(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)
Effects of grain size on the reactivity of limestone temper in a kaolinitic clay
Full text linkCarbonates in clay based ceramics produces higher sintering at lower firing temperatures, but may cause lime spalling, affecting the physical and mechanical behaviour of the ceramic body. The present study investigated the mineralogical and microstructural changes that occur in a kaolinitic clay tempered with different contents of limestone sand with two skewed grain size distributions, after firing. The firing temperatures were set at 500, 750 and 1000 °C. The mineralogy of the fired bodies was analyzed by XRPD and quantitative phase analysis was performed using Rietveld method. SEM-EDS analyses were carried out to investigate the changes in microstructures and the clay/limestone reactivity. The use of sand-sized limestone temper and short firing times induced the formation of non-stoichiometric phases at the clay/limestone boundary, ruled by the lateral variation of CaO activity. The structure and composition of the spinel-type phase (e.g. γ-Al2O3), as typical firing product of kaolinite clays, were investigated. Different Ca-silicates and -aluminosilicates (gehlenite, rankinite and larnite) in ceramics fired at 1000 °C are found according to the limestone grain size. Lime spalling already occurs in ceramics fired at 750 °C; it is triggered by coarse calcined grains (σspalling > σmatrix failure) and then fractures propagates through finer calcined limestone grains
Description of phase V as a combination of modules from pavonite and lillianite homologous series
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