scholarly journals Acmonidesite, a new ammonium sulfate chloride from La Fossa crater, Vulcano, Aeolian Islands, Italy

2018 ◽  
Vol 83 (1) ◽  
pp. 137-142 ◽  
Author(s):  
Francesco Demartin ◽  
Carlo Castellano ◽  
Italo Campostrini
Keyword(s):  
Three Dimensional ◽  
Dimensional Structure ◽  
New Mineral ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
Chlorine Atoms ◽  
Calculated Density ◽  
Sulfate Ions ◽  
Aeolian Islands ◽  
Fossa Crater

AbstractThe new mineral acmonidesite, (NH4,K,Pb2+,Na)9Fe42+(SO4)5Cl8, was found in an active fumarole (fumarole FA, temperature ~250°C) at La Fossa crater, Vulcano, Aeolian Islands, Sicily, Italy. It occurs on a pyroclastic breccia as brown prismatic crystals up to 0.10 mm long, in association with salammoniac, alunite and adranosite. The mineral is orthorhombic, space group C2221 (no. 20) with a = 9.841(1), b = 19.448(3) c = 17.847(3) Å, V = 3415.7(9) Å3 and Z = 4. The six strongest reflections in the powder X-ray diffraction pattern are: [dobs in Å(I)(hkl)] 8.766(100)(110), 1.805(88)(390), 5.178(45)(131), 4.250(42)(221), 2.926(42)(330) and 2.684(32)(261). The empirical formula (based on 28 anions per formula unit [pfu]) is (NH4)5.77K1.42Pb0.62Na1.24Fe3.96Mn0.08S5.04O20.16Cl7.97Br0.08. The idealised formula is (NH4,K,Pb2+,Na)9Fe42+(SO4)5Cl8. The calculated density is 2.551 g cm–3. Using single-crystal diffraction data, the structure was refined to a final R(F) = 0.0363 for 4614 independent observed reflections [I > 2σ(I)]. The structure contains two independent, distorted octahedral iron sites, Fe1 and Fe2, with the iron atoms in the 2+ oxidation state, as confirmed by the interatomic distances and bond-valence calculations (2.06 and 1.94 vu, respectively). Fe1 is surrounded by two chlorine atoms and four oxygens of the sulfate ions, with the following average distances (Å): Fe1–O 2.125 and Fe1–Cl 2.472; and Fe2 is surrounded by three chlorine atoms and three oxygens of the sulfate ions, with the following average distances (Å): Fe2–O 2.110 and Fe2–Cl 2.531. Three independent sulfate anions are also present and are connected with the iron polyhedra to form a three-dimensional structure containing voids occupied by four independent ammonium ions (two of them partially replaced by K+), one Na+/Pb2+ site and one Cl– ion.

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

2014 ◽  
Vol 78 (7) ◽  
pp. 1629-1645 ◽  
Author(s):  
Anna Garavelli ◽  
Daniela Pinto ◽  
Donatella Mitolo ◽  
Luca Bindi
Keyword(s):  
New Mineral ◽  
Volcanic Gases ◽  
Monoclinic Space Group ◽  
Chemical Formula ◽  
X Ray Diffraction ◽  
Sulfate Ion ◽  
Calculated Density ◽  
Aeolian Islands ◽  
X Ray ◽  
Fossa Crater

AbstractLeguernite, 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, balićžunićite 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)Σ=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)º, 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) (11), 2.83 (30) (020), 2.931 (25) (302), 2.502 (25) (04), 2.035 (20) (322), 1.875 (20) (24) and 5.040 (15) (110).The name is in honour of Franc¸ois “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).

Campostriniite, (Bi3+,Na)3(NH4,K)2Na2(SO4)6·H2O, a new sulfate isostructural with görgeyite, from La Fossa Crater, Vulcano, Aeolian Islands, Italy

2015 ◽  
Vol 79 (4) ◽  
pp. 1007-1018 ◽  
Author(s):  
Francesco Demartin ◽  
Carlo Castellano ◽  
Carlo Maria Gramaccioli
Keyword(s):  
General Position ◽  
New Mineral ◽  
Monoclinic Space Group ◽  
Fold Axis ◽  
X Ray Diffraction ◽  
Single Crystal Diffraction ◽  
Calculated Density ◽  
Aeolian Islands ◽  
Na Ions ◽  
Fossa Crater

AbstractThe new mineral campostriniite, (Bi3+,Na)3(NH4,K)2Na2(SO4)6·H2O, was found in an active fumarole (fumarole FA, temperature ∼350°C) at La Fossa Crater, Vulcano, Aeolian Islands, Sicily, Italy. It occurs on a pyroclastic breccia as white prismatic crystals up to 0.2 mm long, in association with adranosite, demicheleite-(Br), demicheleite-(I), argesite and sassolite. The mineral is monoclinic, space group: C2/c (no. 15) with a = 17.748(3), b = 6.982(1) c = 18.221(3) Å, β = 113.97(1)°, V = 2063(1) Å3 and Z = 4. The six strongest reflections in the powder X-ray diffraction pattern are: [dobs in Å (I)(hkl)] 6.396(100)(110), 7.507(75)(202), 2.766(60)(316), 3.380(57)(312), 5.677(55)(111), 3.166(50)(4 0 2). The empirical formula (based on 25 anions p.f.u.) is Bi2.41N1.52Na2.41K0.48 S6.07H8.08O25. The calculated density is 3.87 g cm–3. Using single-crystal diffraction data, the structure was refined to a final R(F) = 0.051 for 3025 independent observed reflections [I > 2σ(I)]. Campostriniite is isostructural with görgeyite and belongs to the 7.CD group of the Strunz classification system. The structure contains two independent nine-fold coordinated sites, one of them located on a two-fold axis (M1) and the other one in general position (M2) essentially occupied by Bi3+ atoms and minor amounts of Na+ ions, an eight-fold coordinated site fully occupied by Na +ions and another eight-fold coordinated site occupied by NH+4 and K+ ions; three independent sulfate anions in a general position and a water molecule coordinated to M1 and located on a two-fold axis are also present.

Demicheleite-(I), BiSI, a new mineral from La Fossa Crater, Vulcano, Aeolian Islands, Italy

2010 ◽  
Vol 74 (1) ◽  
pp. 141-145 ◽  
Author(s):  
F. Demartin ◽  
C. M. Gramaccioli ◽  
I. Campostrini
Keyword(s):  
Unit Cell ◽  
Crystal Habit ◽  
New Mineral ◽  
Orthorhombic Space Group ◽  
Medium Temperature ◽  
Synthetic Compound ◽  
Calculated Density ◽  
Cell Data ◽  
Unit Cell Data ◽  
Fossa Crater

AbstractDemicheleite-(I), ideally BiSI, is the iodine-dominant analogue of demicheleite-(Br) and demicheleite-(Cl). It was found in an active medium-temperature intracrateric fumarole at La Fossa crater, Vulcano Island, Aeolian archipelago, Sicily, Italy. The mineral is the first bismuth sulphoiodide so far discovered in a wholly natural environment, and corresponds to the already known synthetic compound. It occurs as acicular to stout, translucent crystals up to 0.25 mm long in an altered pyroclastic breccia, together with demicheleite-(Br), bismoclite, bismuthinite, godovikovite, panichiite, aiolosite, brontesite, adranosite and other new phases under study. The colour is dark red to black, the lustre submetallic. The unit cell is orthorhombic, space group Pnam, with a = 8.4501(7) Å, b = 10.1470(9) Å , c = 4.1389(4) Å , V = 354.88(4) Å3, and Z = 4. The crystal habit is prismatic, with the main forms {110} and {111} inferred from analogy with demicheleite-(Br). Twinning was not observed. The strongest 6 lines in the X-ray powder diffraction pattern [dobs.(Å) (I/I0) (hkl)] are: 6.490 (100) (110); 4.346 (94) (120); 3.896 (90) (210); 2.709 (60) (310); 2.161 (38) (330); 3.243 (22) (220). The chemical analysis obtained by WDS electron microprobe gave: Bi 58.32, S 9.43, I 23.69, Br 5.66, Cl 1.01, totalling 98.11 wt.%, corresponding to an empirical formula (based on 3 a.p.f.u.) of: Bi0.97S1.03(I0.65Br0.25Cl0.10)Σ1.00. The unit-cell data are close to those of the synthetic compound, whose crystal structure is already known. The calculated density is 6.411 g cm–3.

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

2014 ◽  
Vol 78 (4) ◽  
pp. 1043-1055 ◽  
Author(s):  
D. Pinto ◽  
A. Garavelli ◽  
D. Mitolo
Keyword(s):  
New Mineral ◽  
Average Chemical Composition ◽  
Calculated Density ◽  
Triclinic Space Group ◽  
Aeolian Islands ◽  
History Museum ◽  
X Ray ◽  
The University ◽  
Fossa Crater ◽  
Fumarole Sublimate

AbstractBalićžunićite, 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 μm across and up to 200 μm 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 P, with a 6.7386(3), b 11.1844(5), c 14.1754(7) Å, α 80.082(2)°, β 88.462(2)°, γ 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) (01), 3.366 (7) (200), 5.562 (4) (11), 5.433 (4) (111). 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).

scholarly journals Hansesmarkite, Ca2Mn2Nb6O19·20H2O, a new hexaniobate from a syenite pegmatite in the Larvik Plutonic Complex, southern Norway

2017 ◽  
Vol 81 (3) ◽  
pp. 543-554 ◽  
Author(s):  
H. Friis ◽  
M. T. Weller ◽  
A. R. Kampf
Keyword(s):  
Three Dimensional ◽  
Dimensional Structure ◽  
New Mineral ◽  
Optical Orientation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Naturally Occurring ◽  
Plutonic Complex ◽  
Diffraction Diagram ◽  
Southern Norway

AbstractThe new mineral hansesmarkite (IMA2015-067), Ca2Mn2Nb6O19·20H2O, was discovered at the AS Granit larvikite quarry in Tvedalen, Larvik, Vestfold, Norway. Hansesmarkite forms faintly yellow crystals up to 0.3 mm or thin coatingsin patches on gonnardite. Hansesmarkite is biaxial (+) with refractive indices (white light): α = 1.683(2), β = 1.698(2) and γ = 1.745(3); 2V(meas.) = 60.7(6)° and 2V(calc.) = 60.3°. The mineral exhibits moderate dispersion (r > v)and is pleochroic with X (almost colourless) < Y ( pale yellow) << Z (orangey yellow). The optical orientation is X ^ c = 20°, Y ^ b = 16° and Z ^ a = 5°. The empirical formula based on five electron probemicroanalyses and calculated based on Nb = 6 apfu is (Ca1.93Na0.02K0.01)∑1.96(Mn1.79Fe0.11)∑1.90Nb6O18.84·20H2O, with H2O determined from the structure solution.The mineral is triclinic, P1, with a = 9.081(4), b = 9.982(8), c = 10.60(1) Å, α = 111.07(8), β = 101.15(6), γ = 99.39(5)°, V = 850.8(13) Å3 and Z = 1. The structure was solved at 120 K because of thermalinstability of the mineral and refined to R1 = 2.50% for Fo > 4σ. The strongest reflections in the x-ray diffraction diagram are: [dobs. in Å (I)(hkl)] 9.282(36)(001), 8.610(100)(100, 011), 3.257(30)(031, 131)and 3.058(18)(130, 212). Hansesmarkite is the third naturally occurring hexaniobate in which six edge-sharing Nb-octahedra form the Lindqvist ion. These are linked via Mn-octahedra forming rods along [100] and Ca is located between the rods, creating a three dimensional structure via hydrogen bonds.

Currierite, Na4Ca3MgAl4(AsO3OH)12·9H2O, a new acid arsenate with ferrinatrite-like heteropolyhedral chains from the Torrecillas mine, Iquique Province, Chile

2017 ◽  
Vol 81 (5) ◽  
pp. 1141-1149 ◽  
Author(s):  
Anthony R. Kampf ◽  
Stuart J. Mills ◽  
Barbara P. Nash ◽  
Maurizio Dini ◽  
Arturo A. Molina Donoso
Keyword(s):  
Room Temperature ◽  
Three Dimensional ◽  
Geometrical Isomer ◽  
New Mineral ◽  
X Ray Diffraction ◽  
Calculated Density ◽  
Secondary Alteration ◽  
Crystal Forms ◽  
X Ray ◽  
Mohs Hardness

AbstractThe new mineral currierite (IMA2016-030), Na4Ca3MgAl4(AsO3OH)12·9H2O, was found at the Torrecillas mine, Iquique Province, Chile, where it occurs as a secondary alteration phase in association with anhydrite, canutite, chudobaite, halite, lavendulan, magnesiokoritnigite, quartz, scorodite and torrecillasite. Currierite occurs as hexagonal prisms, needles and hair-like fibres up to ∼200 μm long, in sprays. The crystal forms are ﹛100﹜ and ﹛001﹜. Crystals are transparent, with vitreous to silky lustre and white streak. The Mohs hardness is ∼2, tenacity is brittle, but elastic in very thin fibres, and the fracture is irregular. Crystals exhibit at least one good cleavage parallel [001]. The measured density is 3.08(2) g cm -3 and the calculated density is 3.005 g cm -3. Optically, currierite is uniaxial (–) with ω= 1.614(1) and ε= 1.613(1) (measured in white light). The mineral is slowly soluble in dilute HCl at room temperature. The empirical formula, determined from electron-microprobe analyses, is (Na3.95A12.96Ca2.74Mg1.28Fe0.633+Cu0.13K0.08Co0.03Σ11.80 (AS11.685+Sb0.325+Σ12(O56.96Cl0.04)Σ57H30.81. Currierite is hexagonal, P622, with a = 12.2057(9), c = 9.2052(7) Å, V= 1187.7(2) Å3 and Z = 1. The eight strongest powder X-ray diffraction lines are [dobs Å(I)(hkl)]: 10.63(100)(100), 6.12(20)(110), 5.30(15)(200), 4.61(24)(002), 4.002(35)(210), 3.474(29)(202), 3.021(96)(212) and 1.5227(29)(440,334,612). The structure of currierite (R1 = 2.27% for 658 Fo > 4σF reflections) is based upon a heteropolyhedral chain along c in which AlO6 octahedra are triple-linked by sharing corners with AsO3OH tetrahedra. Chains are linked to one another by bonds to 8(4 + 4)-coordinated Na and 8-coordinated Ca forming a three-dimensional framework with large cavities that contain rotationally disordered Mg(H2O)6 octahedra. The chain in the structure of currierite is identical to that in kaatialaite and a geometrical isomer of that in ferrinatrite. The mineral is named in honour of Mr. Rock Henry Currier (1940–2015), American mineral dealer, collector, author and lecturer.

Aluminopyracmonite, (NH4)3Al(SO4)3, a new ammonium aluminium sulfate from La Fossa crater, Vulcano, Aeolian Islands, Italy

2013 ◽  
Vol 77 (4) ◽  
pp. 443-451 ◽  
Author(s):  
F. Demartin ◽  
C. Castellano ◽  
I. Campostrini
Keyword(s):  
New Mineral ◽  
Single Crystal Diffraction ◽  
Medium Temperature ◽  
Synthetic Compound ◽  
Calculated Density ◽  
Aeolian Islands ◽  
X Ray ◽  
Aluminium Sulfate ◽  
The Difference ◽  
Fossa Crater

AbstractThe new mineral aluminopyracmonite, ideally (NH4)3Al(SO4)3, was found in a medium-temperature (∼250°C) intracrater active fumarole at La Fossa crater, Vulcano, Aeolian Islands, Sicily, Italy. It occurs on a pyroclastic breccia as colourless to white prismatic crystals up to 0.2 mm long, in association with adranosite, mascagnite, alunite and salammoniac. The mineral is identical to the synthetic compound (NH4)3Al(SO4)3. It is trigonal, space group: R (no. 148) with a = 15.0324(8), c = 8.8776(5) 5, V = 1737.3(2) Å3 and Z = 6. The six strongest reflections in the X-ray powder diffraction pattern are: [dobs in Å (I)(hkl)] 3.336(100)(131), 7.469(62)(1 1 0), 3.288(60)(122), 4.289(45)(31), 2.824(29)(51), 4.187(27) (012). The empirical formula based on 12 anions is [(NH4)2.89K0.10]Σ 2.99(Al1.18Fe0.01)Σ 1.19S2.91O12, and the simplified formula (NH4,K)3Al(SO4)3. The measured density is 2.12(1) g/cm3, calculated density 2.143 g/cm3. The mineral is uniaxial(–) with ω = 1.545(3) and ε = 1.532(3) (λ = 589 nm). Using single-crystal diffraction data, the structure was refined to a final R(F) = 0.0258 for 998 independent observed reflections [I > 2σ(I)]. In spite of having unitcell parameters comparable with those of pyracmonite, the two minerals are not isostructural; the difference is related to a disordered conformation of the sulfate anions about the two independent Al3+ ions in aluminopyracmonite.

Chinleite-(Y), NaY(SO4)2·H2O, a new rare-earth sulfate mineral structurally related to bassanite

2017 ◽  
Vol 81 (4) ◽  
pp. 909-916 ◽  
Author(s):  
Anthony R. Kampf ◽  
Barbara P. Nash ◽  
Joe Marty
Keyword(s):  
Room Temperature ◽  
Three Dimensional ◽  
New Mineral ◽  
X Ray Diffraction ◽  
Calculated Density ◽  
Secondary Alteration ◽  
X Ray ◽  
Mohs Hardness ◽  
San Juan County ◽  
Bow Tie

AbstractThe new mineral chinleite-(Y) (IMA2016-017), NaY(SO4)2·H2O, was found in the Blue Lizard mine, San Juan County, Utah, USA, where it occurs as a secondary alteration phase. Chinleite-(Y) crystals are thin hexagonal {100} prisms (up to 0.3 mm long) with pyramidal terminations consisting of the forms {101} and {011}. Prisms are typically intergrown in divergent sprays, bow-tie aggregates or subparallel intergrowths. Crystals are colourless and transparent with a vitreous lustre. The streak is white and the mineral is nonfluorescent. The Mohs hardness is between 2½ and 3. Crystals are brittle with at least one good cleavage parallel to [001], probably {100}, and have splintery fracture. The mineral is slowly soluble in H2O at room temperature. The calculated density is 3.385 g cm–3. The mineralis optically uniaxial (+), with ω = 1.565(1) and ε = 1.603(1) (white light). Electron microprobe analyses yielded the empirical formula (Na0.507Ca0.285Y0.176)∑0.968(Y0.724Dy0.110Er0.053Gd0.037Ho0.021Yb0.013Nd0.014Eu0.005Sm0.008Ce0.010Pr0.003La0.002)∑1.000(SO4)2·H1.401O.The eight strongest powder X-ray diffraction lines are [dobs Å(I)(hkl)]: 6.01(59)(100), 5.43(63)(011), 3.457(46)(110), 3.010(100)(200), 2.826(95)(014), 2.1365(39)(006,122), 1.8493(67)(214) and 1.6901(28)(125,034). Chinleite-(Y) is trigonal, P3221,a = 6.890(2), c = 12.767(2) Å, V = 524.9(3) Å3 and Z = 3. The structure of chinleite-(Y) (R1 = 0.0444 for 303 Fo > 4σF), a three-dimensional framework, consisting of SO4 groups, irregular NaO8 polyhedra and YO9 distorted tricapped trigonal prisms, is similar to the structure of bassanite.

The crystal and molecular structure of adenosine triphosphate

1971 ◽  
Vol 325 (1562) ◽  
pp. 401-436 ◽  
Keyword(s):  
Adenosine Triphosphate ◽  
Three Dimensional ◽  
Direct Methods ◽  
Disodium Salt ◽  
Dimensional Structure ◽  
Water Molecules ◽  
Sodium Ions ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
Centrosymmetric Dimer

The three-dimensional structure of the hydrated disodium salt of adenosine triphosphate (Na 2 ATP) has been determined from an X-ray diffraction study to a resolution of 0.9 Å. The crystals are orthorhombic, space group P 2 1 2 1 2 1 , with a = 30.45(4), b = 20.88(3), c = 7.07(1) Å. There are two molecules of ATP, four sodium ions, and six water molecules in the asymmetric unit. The structure was solved by direct methods and refined to R = 12.3 % using 1118 intensities measured on an automatic diffractometer. The triphosphate chain is in the folded conformation in each of the two crystallographically independent molecules. However, in one molecule (A) it is folded so as to form part of a lefthanded helix, while in the other part of a right-handed helix. There are corresponding differences in the conformations of the ribose rings. The ring is in the envelope conformation with C3' endo in molecule A and C2' endo in molecule B. Two of the sodium ions coordinate the two molecules through the phosphate oxygens and N7 to form an almost centrosymmetric ‘dimer’ which is the fundamental structural unit. The adenine bases show considerable overlap and are stacked in the c axis direction. Details of the hydrogen bonding and the role of water molecules in the structure are discussed.

scholarly journals Tazzoliite: a new mineral with a pyrochlore-related structure from the Euganei Hills, Padova, Italy

2012 ◽  
Vol 76 (4) ◽  
pp. 827-838 ◽  
Author(s):  
F. Cámara ◽  
F. Nestola ◽  
L. Bindi ◽  
A. Guastoni ◽  
F. Zorzi ◽  
...  
Keyword(s):  
Pyrochlore Structure ◽  
New Mineral ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
Orthorhombic Space Group ◽  
Calculated Density ◽  
Oh Groups ◽  
X Ray ◽  
Cell Parameters ◽  
Perfect Cleavage

AbstractTazzoliite, ideally Ba2CaSr0.5Na0.5Ti2Nb3SiO17[PO2(OH)2]0.5, is a new mineral (IMA 2011-018) from Monte delle Basse, Euganei Hills, Galzignano Terme, Padova, Italy. It occurs as lamellar pale orange crystals, which are typically a few m m thick and up to 0.4 mm long, closely associated with a diopsidic pyroxene and titanite. Tazzoliite is transparent. It has a white streak, a pearly lustre, is not fluorescent and has a hardness of 6 (Mohs' scale). The tenacity is brittle and the crystals have a perfect cleavage along {010}. The calculated density is 4.517 g cm–3. Tazzoliite is biaxial (–) with 2Vmeas of ~50º, it is not pleochroic and the average refractive index is 2.04. No twinning was observed. Electronmicroprobe analyses gave the following chemical formula: (Ba1.93Ca1.20Sr0.52Na0.25Fe0.102+)Σ4 (Nb2.88Ti2.05Ta0.07Zr0.01V0.015+)Σ5.02SiO17[(P0.13Si0.12S0.07)Σ0.32O0.66(OH)0.66][F0.09(OH)0.23]Σ0.32.Tazzoliite is orthorhombic, space group Fmmm, with unit-cell parameters a = 7.4116(3), b = 20.0632(8), c = 21.4402(8) Å, V = 3188.2(2) Å3 and Z = 8. The crystal structure, obtained from single-crystal X-ray diffraction data, was refined to R1(F2) = 0.063. It consists of a framework of Nb(Ti) octahedra and BaO7 polyhedra sharing apexes or edges, and Si tetrahedra sharing apexes with Nb(Ti) octahedra and BaO7 polyhedra. The structure, which is related to the pyrochlore structure, contains three Nb(Ti) octahedra: two are Nb dominant and one is Ti dominant. Chains of A2O8 polyhedra [A2 being occupied by Sr(Ca, Fe)] extend along [100] and are surrounded by Nb octahedra. Channels formed by six Nb(Ti) octahedra and two tetrahedra, or four A1O8(OH) polyhedra (A1 being occupied by Ba), alternate along [100]. The channels are partially occupied by [PO2(OH)2] in two possible mutually exclusive positions, alternating with fully occupied A3O7 polyhedral pairs [A3 being occupied by Ca(Na)]. The seven strongest X-ray powder diffraction lines [d in Å (I/I0) (hkl)] are: 3.66 (60) (044), 3.16 (30) (153), 3.05 (100) (204), 2.98 (25) (240), 2.84 (50) (064), 1.85 (25) (400) and 1.82 (25) (268). Raman spectra of tazzoliite were collected in the range 150–3700 cm–1 and confirm the presence of OH groups. Tazzoliite is named in honour of Vittorio Tazzoli in recognition of his contributions to the fields of mineralogy and crystallography.

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