Redgillite, Cu6(OH)10(SO4)·H2O, a new mineral from Caldbeck Fells, Cumbria, England: description and crystal structure

2005 ◽  
Vol 69 (6) ◽  
pp. 973-980 ◽  
Author(s):  
J. J. Pluth ◽  
I. M. Steele ◽  
A. R. Kampf ◽  
D. I. Green
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Cross Section ◽  
New Mineral ◽  
Calculated Density ◽  
Oh Groups ◽  
X Ray ◽  
Jahn Teller ◽  
Mohs Hardness ◽  
Measured Density

AbstractRedgillite, Cu6(OH)10(SO4)·H2O, space group P21/c, a 3.155(3) Å, b 10.441(8) Å, c 19.436(16) Å, β 90.089(13)°, V = 640.2(9) Å3, Z = 2, is a new mineral from Silver Gill, Caldbeck Fells, Cumbria, England. The strongest six lines of the X-ray powder-diffraction pattern [d in Å, (I)(hkl)] are: 9.72 (90) (002), 7.11 (100) (012), 4.60 (30) (022), 4.068 (20) (023), 2.880 (30) (112,112̄), 2.318 (50) (131,131̄). It occurs as translucent to transparent grass-green bladed crystals up to 0.15 mm long with squared-off or tapering terminations; usually in radiating groups. Forms observed are {001} prominent, {010} as composite stepped faces, and {100} irregular. Redgillite has white streak, vitreous lustre and Mohs hardness of ∼2. Blades are slightly flexible with irregular fracture and exhibit a perfect {001} cleavage and good {100} and {010} cleavages. The measured density (by sink-float) is 3.45(5) g/cm3; the calculated density is 3.450 g/cm3. The mineral dissolves slowly in dilute HCl. Redgillite is biaxial- negative with α = 1.693(2), β = 1.721(2), γ = 1.723(2), 2V = 30(2)° (meas.) and 30° (calc.); dispersion is r > v, medium; pleochroism: Y blue-green α X blue-green α Z yellow-green; orientation: X ≈ c , Y = b, Z ≈ a. Electron microprobe analyses yielded CuO 68.9, SO3 11.6, total 80.5. With water inferred from the structure analysis, the empirical formula is: Cu5.995(OH)9.991(SO4)1.003·H2O. Redgillite is typically found in thin fractures in partly oxidized sulphides where it is commonly associated with langite and more rarely with malachite, cuprite, connellite and brochantite. The name is for the Red Gill mine, from which the mineral is best known. The crystal structure of redgillite was determined and refined to R = 0.090 for 1529 observed reflections [I > 2σ(I)]. The redgillite structure consists of Jahn-Teller distorted CuO6 octahedra and SO4 tetrahedra. The octahedra share edges to form sheets that are zig-zag in cross section. The SO4 tetrahedra share an oxygen with the Cu layer and link the layers by hydrogen bonds to OH groups. The crystal structures of wroewolfeite, langite, posnjakite, spangolite and schulenbergite are similar to redgillite. They all contain edge sharing CuO6 layers connected to SO4 groups with the layers bridged via hydrogen bonds.

Cuyaite, Ca2Mn3+As3+14O24Cl, a new mineral with an arsenite framework from near Cuya, Camarones Valley, Chile.

2020 ◽  
Vol 84 (3) ◽  
pp. 477-484
Author(s):  
Anthony R. Kampf ◽  
Stuart J. Mills ◽  
Barbara Nash ◽  
Maurizio Dini ◽  
Arturo A. Molina Donoso
Keyword(s):  
Crystal Structure ◽  
Raman Spectrum ◽  
Meteoric Water ◽  
New Mineral ◽  
X Ray Diffraction ◽  
Calculated Density ◽  
X Ray ◽  
Jahn Teller ◽  
Mohs Hardness ◽  
3D Framework

AbstractCuyaite (IMA2019-126), Ca2Mn3+As3+14O24Cl, is a new arsenite mineral from near Cuya in the Camarones Valley, Arica Province, Chile. It is associated with anhydrite, native arsenic, arsenolite, calcite, claudetite, ferrinatrite, gajardoite-3R, leiteite, magnesiocopiapite, phosphosiderite, pyrite, realgar and talmessite and formed from the oxidation of As-bearing primary phases and alteration by saline fluids derived from evaporating meteoric water under hyperarid conditions. Cuyaite occurs as pale brown thin needles (elongated on [010]), typically in divergent sprays and subparallel intergrowths. The streak is white. Crystals are transparent with adamantine lustre; subparallel intergrowths exhibit silky lustre. The mineral has Mohs hardness of 2½, is brittle, exhibits no cleavage and has irregular fracture. The calculated density is 4.140 g cm–3. Cuyaite is optically biaxial (–), with α = 1.87(1), β = 1.956(calc) and γ = 1.98(1), determined in white light; 2Vmeas = 60(1)°; and orientation: X = b and Y ^ a = 53° in obtuse β. Electron microprobe analyses provided the empirical formula Ca2.03Mn3+0.95(As3+13.66Sb3+0.65)Σ14.31O24Cl0.88. The six strongest powder X-ray diffraction lines are [dobs Å(I)(hkl)]: 4.73(45)(111, $\bar{1}$12), 3.162(100)($\bar{3}$14), 3.035(28)(213), 3.004(37)(204), 2.931(90)($\bar{2}$15, 312) and 2.779(28)(020). Cuyaite is monoclinic, Pn, a = 14.7231(6), b = 5.58709(19), c = 17.4185(12) Å, β = 112.451(8)°, V = 1324.23(14) Å3 and Z = 2. In the crystal structure of cuyaite (R1 = 0.0369 for 2095 I > 2σI reflections), AsO3 pyramids share O corners to form a ‘loose’ 3D framework; Jahn–Teller distorted Mn3+O6 octahedra and CaO8 polyhedra link by edges and corners to form columns; the columns also link by edge- and corner-sharing to the AsO3 pyramids in the framework; Cl occupies channels along [010] in the framework. The Raman spectrum is consistent with the presence of multiple As3+O3 groups.

scholarly journals Parisite-(La), ideally CaLa2(CO3)3F2, a new mineral from Novo Horizonte, Bahia, Brazil

2018 ◽  
Vol 82 (1) ◽  
pp. 133-144 ◽  
Author(s):  
Luiz A. D. Menezes Filho ◽  
Mario L. S. C. Chaves ◽  
Nikita V. Chukanov ◽  
Daniel Atencio ◽  
Ricardo Scholz ◽  
...  
Keyword(s):  
Single Crystal ◽  
Ir Spectrum ◽  
Empirical Formula ◽  
New Mineral ◽  
Formula Unit ◽  
Calculated Density ◽  
Oh Groups ◽  
Space Group ◽  
X Ray ◽  
Mohs Hardness

ABSTRACTParisite-(La) (IMA2016-031), ideally CaLa2(CO3)3F2, occurs in a hydrothermal vein crosscutting a metarhyolite of the Rio dos Remédios Group, at the Mula mine, Tapera village, Novo Horizonte county, Bahia, Brazil, associated with hematite, rutile, almeidaite, fluocerite-(Ce), brockite, monazite-(La), rhabdophane-(La) and bastnäsite-(La). Parisite-(La) occurs as residual nuclei (up to 5 mm) in steep doubly-terminated pseudo-hexagonal pyramidal crystals (up to 8.2 cm). Parisite-(La) is transparent, yellow-green to white, with a white streak and displays a vitreous (when yellow-green) to dull (when white) lustre. Cleavage is distinct on pseudo-{001}; fracture is laminated, conchoidal, or uneven. The Mohs hardness is 4 to 5, and it is brittle. Calculated density is 4.273 g cm−3. Parisite-(La) is pseudo-uniaxial (+), ω = 1.670(2) and ε = 1.782(5) (589 nm). The empirical formula normalized on the basis of 11 (O + F) atoms per formula unit (apfu) is Ca0.98(La0.83Nd0.51Ce0.37Pr0.16Sm0.04Y0.03)Σ1.94C3.03O8.91F2.09. The IR spectrum confirms the absence of OH groups. Single-crystal X-ray studies gave the following results: monoclinic (pseudo-trigonal), space group: C2, Cm, or C2/m, a = 12.356(1) Å, b = 7.1368(7) Å, c = 28.299(3) Å, β = 98.342(4)°, V = 2469.1(4) Å3 and Z = 12. Parisite-(La) is the La-dominant analogue of parisite-(Ce).

Torrecillasite, Na(As,Sb)43+O6Cl, a new mineral from the Torrecillas mine, Iquique Province, Chile: description and crystal structure

2014 ◽  
Vol 78 (3) ◽  
pp. 747-755 ◽  
Author(s):  
A. R. Kampf ◽  
B. P. Nash ◽  
M. Dini ◽  
A. A. Molina Donoso
Keyword(s):  
Cross Section ◽  
New Mineral ◽  
Optical Orientation ◽  
Calculated Density ◽  
Secondary Alteration ◽  
X Ray ◽  
Mohs Hardness ◽  
Cl Atoms ◽  
Shaped Cross Section ◽  
Irregular Cleavage

AbstractThe new mineral torrecillasite (IMA2013-112), Na(As,Sb)43+O6Cl, was found at the Torrecillas mine, Iquique Province, Chile, where it occurs as a secondary alteration phase in association with anhydrite, cinnabar, gypsum, halite, lavendulan, magnesiokoritnigite, marcasite, quartz, pyrite, scorodite, wendwilsonite and other potentially new As-bearing minerals. Torrecillasite occurs as thin colourless prisms up to 0.4 mm long in jack-straw aggregates, as very thin fibres in puff balls and as massive intergrowths of needles. Prisms are elongated on [100] with diamond-shaped cross-section and irregular terminations. Crystals are transparent, with adamantine lustre and white streak. The Mohs hardness is 2½, tenacity is brittle and fracture is irregular. Cleavage on (001) is likely. The calculated density is 4.056 g cm−3. Optically, torrecillasite is biaxial (−) with α = 1.800(5), β = 1.96(1), γ = 2.03(calc.) (measured in white light). The measured 2V is 62.1(5)°, no dispersion or pleochroism were observed, the optical orientation isX=c,Y=b,Z=a. The mineral is very slowly soluble in H2O, slowly soluble in dilute HCl and rapidly soluble in concentrated HCl. The empirical formula, determined from electron-microprobe analyses, is (Na1.03Mg0.02)∑1.05(As3.39Sb0.62)∑4.01O6.07Cl0.93. Torrecillasite is orthorhombic,Pmcn, a= 5.2580(9),b= 8.0620(13),c= 18.654(3) Å,V= 790.7(2) Å3andZ= 4. The eight strongest X-ray powder diffraction lines are [dobsÅ(I)(hkl)]: 4.298(33)(111), 4.031(78)(014,020), 3.035(100)(024,122), 2.853(39)(115,123), 2.642(84)(124,200), 2.426(34)(125), 1.8963(32)(225) and 1.8026(29)(0·1·10,233). The structure, refined toR1= 4.06% for 814Fo>4σFreflections, contains a neutral, wavy As2O3layer parallel to (001) consisting of As3+O3pyramids that share O atoms to form six-membered rings. Successive layers are flipped relative to one another and successive interlayer regions contain alternately either Na or Cl atoms. Torrecillasite is isostructural with synthetic orthorhombic NaAs4O6Br.

Hydroniumpharmacosiderite, a new member of the pharmacosiderite supergroup from Cornwall, UK: structure and description

2010 ◽  
Vol 74 (5) ◽  
pp. 863-869 ◽  
Author(s):  
S. J. Mills ◽  
A. R. Kampf ◽  
P. A. Williams ◽  
P. Leverett ◽  
G. Poirier ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Diffraction Pattern ◽  
Powder Diffraction ◽  
Empirical Formula ◽  
Direct Methods ◽  
Structure Type ◽  
New Mineral ◽  
Calculated Density ◽  
X Ray ◽  
Mohs Hardness

AbstractHydroniumpharmacosiderite, ideally (H3O)Fe4(AsO4)3(OH)4·4H2O, is a new mineral from Cornwall, UK, probably from the St. Day group of mines. It occurs as a single yellowish green, slightly elongated cube, measuring 0.17 mm ×0.14 mm ×0.14 mm. The mineral is transparent with a vitreous lustre. It is brittle with a cleavage on {001}, has an irregular fracture, a white streak and a Mohs hardness of 2–3 (determined on H3O-exchanged pharmacosiderite). Hydroniumpharmacosiderite has a calculated density of 2.559 g cm–3 for the empirical formula. The empirical formula, based upon 20.5 oxygen atoms, is: [(H3O)0.50K0.48Na0.06]1.04(Fe3.79Al0.22)4.01[(As2.73P0.15)2.88O12](OH)4·4H2.14O. The five strongest lines in the X-ray powder diffraction pattern are [dobs(Å),Iobs,(hkl)]: 8.050,100,(001); 3.265,35,(112); 2.412,30,(113); 2.830,23,(202); 4.628,22,(111). Hydroniumpharmacosiderite is cubic, space group with a = 7.9587(2) Å, V = 504.11(2) Å3 and Z = 1. The crystal structure was solved by direct methods and refined to R1 = 0.0481 for 520 reflections with I > 2σ(I). The structure is consistent with determinations for H3O-exhchanged pharmacosiderite and the general pharmacosiderite structure type.

Gajardoite, KCa0.5As3+4O6Cl2·5H2O, a new mineral related to lucabindiite and torrecillasite from the Torrecillas mine, Iquique Province, Chile

2016 ◽  
Vol 80 (7) ◽  
pp. 1265-1272 ◽  
Author(s):  
Anthony R. Kampf ◽  
Barbara P. Nash ◽  
Maurizio Dini ◽  
Arturo Molina A. Donoso
Keyword(s):  
Electron Microprobe ◽  
Room Temperature ◽  
New Mineral ◽  
X Ray Diffraction ◽  
Calculated Density ◽  
Secondary Alteration ◽  
X Ray ◽  
Mohs Hardness ◽  
Measured Density ◽  
Irregular Cleavage

AbstractThe new mineral gajardoite (IMA2015-040), KCa0.5As3+4O6Cl2·5H2O, was found at the Torrecillas mine, Iquique Province, Chile, where it occurs as a secondary alteration phase in association with native arsenic, arsenolite,chongite, talmessite and torrecillasite. Gajardoite occurs as hexagonal plates up to ∼100 μm in diameter and 5 μm thick, in rosette-like subparallel intergrowths. Crystals are transparent, with vitreous lustre and white streak. The Mohs hardness is ∼1½, tenacity is brittleand fracture is irregular. Cleavage is perfect on {001}. The measured density is 2.64 g/cm3 and the calculated density is 2.676 g/cm3. Optically, gajardoite is uniaxial (–) with ω = 1.780(3) and ε = 1.570(5) (measured in white light). The mineral is very slowly soluble in H2O and slowly soluble in dilute HCl at room temperature. The empirical formula, determined from electron-microprobe analyses, is (K0.77Ca0.71Na0.05Mg0.05)∑1.58As4O11Cl1.96H9.62.Gajardoite is hexagonal, P6/mmm, a = 5.2558(8), c = 15.9666(18) Å, V = 381.96(13) Å3 and Z = 1. The eight strongest powder X-ray diffraction lines are [dobs Å(I)(hkl)]: 16.00(100)(001), 5.31(48)(003),3.466 (31)(103), 3.013(44)(104), 2.624(51)(006,110,111), 2.353(36)(113), 1.8647(21)(116,205) and 1.4605(17) (119,303,216). The structure, refined to R1 = 3.49% for 169 Fo > 4σF reflections, contains two types of layers. One layer of formulaKAs3+4O6Cl2 consists of two neutral As2O3 sheets, between which are K+ cations and on the outside of which are Cl– anions. This layer is topologically identical to a slice of the lucabindiite structureand similar to a slice of the torrecillasite structure. The second layer consists of an edge-sharing sheet of Ca(H2O)6 trigonal pyramids with isolated H2O groups centred in the hexagonal cavities in the sheet.

Wooldridgeite, Na2(P2O7)2(H2O)10: A new mineral from Judkins Quarry, Warwickshire, England

1999 ◽  
Vol 63 (1) ◽  
pp. 13-16 ◽  
Author(s):  
F. C. Hawthorne ◽  
M. A. Cooper ◽  
D. I. Green ◽  
R. E. Starkey ◽  
A. C. Roberts ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Microprobe Analysis ◽  
Electron Microprobe Analysis ◽  
Infrared Absorption Spectrum ◽  
Short Wave ◽  
New Mineral ◽  
Calculated Density ◽  
X Ray ◽  
Mohs Hardness ◽  
Unit Formula

AbstractWooldridgeite, ideally Na2(P2O7)2(H2O)10, orthorhombic, a = 11.938(1), b = 32.854(2), c = 11.017(1) Å , V = 4321.2(8) Å3, a:b:c = 0.3634:1:0.3353, space group Fdd2, Z = 8, is a new mineral from Judkins Quarry, Nuneaton, Warwickshire, England. Associated minerals are calcite, chalcopyrite, bornite and baryte. It occurs as equant crystals forming rhombic dipyramids; no twinning was observed. It is transparent blue-green with a very pale-blue streak, a vitreous lustre, and does not fluoresce under long- or short-wave ultraviolet light. Wooldridgeite has a Mohs hardness of 2–3, is brittle with an irregular fracture, and has no cleavage. The calculated density is 2.279 g/cm3. In transmitted light, wooldridgeite is colourless, non-pleochroic, and shows no dispersion. It is biaxial negative with α = 1.508(1), β = 1.511(1), γ = 1.517(1), 2V(meas.) = 76.2(5), 2V(calc.) = 71(10)8, X = b, Y = c, Z = a. The strongest five reflections in the X-ray powder diffraction pattern are [d(Å), (I), (hkl)]: 8.23(30)(040), 6.52(100)(131), 4.05(40)(260), 3.255(40)(262); 2.924(40)(371). Electron-microprobe analysis of wooldridgeite gave P2O5 39.37, CuO 20.24, MgO 0.24, CaO 7.73, Na2O 8.33, K2O 0.17, H2O(calc.) 24.72, sum 100.80 wt.%; the corresponding unit formula (based on 24 anions) is (Na1.96K0.03)Ca1.00(Cu1.85Mg0.04)P4.04O14(H2O)10 where the H2O groups were assigned from knowledge of the crystal structure; the infrared absorption spectrum also indicates the presence of H2O in the structure. The mineral is named for James Wooldridge (1923–1995), a fervent amateur mineral collector who discovered this mineral.

Oxyplumboroméite, Pb2Sb2O7, a new mineral species of the pyrochlore supergroup from Harstigen mine, Värmland, Sweden

2013 ◽  
Vol 77 (7) ◽  
pp. 2931-2939 ◽  
Author(s):  
U. Hålenius ◽  
F. Bosi
Keyword(s):  
Crystal Structure ◽  
Structure Refinement ◽  
New Mineral ◽  
Crystal Structure Refinement ◽  
Unit Cell Parameters ◽  
Calculated Density ◽  
X Ray ◽  
Cell Parameters ◽  
New Mineral Species ◽  
Mohs Hardness

AbstractOxyplumboroméite, Pb2Sb2O7, is a new mineral of the roméite group of the pyrochlore supergroup (IMA 2013-042). It is found together with calcite and leucophoenicite in fissure fillings in tephroite skarn at the Harstigen mine, Värmland, Sweden. The mineral occurs as yellow to brownish yellow rounded grains or imperfect octahedra. Oxyplumboroméite has a Mohs hardness of ∼5, a calculated density of 6.732 g/cm3 and is isotropic with a calculated refractive index of 2.061. Oxyplumboroméite is cubic, space group Fdm, with the unit-cell parameters a = 10.3783(6) Å, V = 1117.84(11) Å3 and Z = 8. The strongest five X-ray powder-diffraction lines [d in Å(I)(hkl)] are: 2.9915(100)(222), 2.5928(32)(400), 1.8332(48)(440), 1.5638(38)(622) and 1.1900(12)(662). The crystal structure of oxyplumboroméite was refined to an R1 index of 3.02% using 160 unique reflections collected with MoKα radiation. Electron microprobe analyses in combination with crystal-structure refinement, infrared, Mössbauer and electronic absorption spectroscopy resulted in the empirical formula A(Pb0.92Ca0.87Mn0.09Sr0.01Na0.05)Σ1.93B(Sb1.73Fe3+0.27)Σ2.00X+Y[O6.64(OH)0.03]Σ6.67. Oxyplumboroméite is the Pb analogue of oxycalcioroméite, ideally Ca2Sb2O7.

Fluorapophyllite-(NH4), NH4Ca4(Si8O20)F⋅8H2O, a new member of the apophyllite group from the Vechec quarry, eastern Slovakia

2020 ◽  
Vol 84 (4) ◽  
pp. 533-539
Author(s):  
Martin Števko ◽  
Jiří Sejkora ◽  
Jakub Plášil ◽  
Zdeněk Dolníček ◽  
Radek Škoda
Keyword(s):  
Crystal Structure ◽  
Brittle Fracture ◽  
Powder Diffraction ◽  
Slovak Republic ◽  
The Other ◽  
New Mineral ◽  
Calculated Density ◽  
X Ray ◽  
Perfect Cleavage ◽  
Mohs Hardness

AbstractThe new mineral fluorapophyllite-(NH4), ideally NH4Ca4(Si8O20)F⋅8H2O, was found at the Vechec andesite quarry located near Vechec village, Vranov nad Topľou Co., Prešov Region, Slovak Republic. It occurs in cavities of quartz–illite–saponite–tobelite xenolith embedded in pyroxene andesite. Fluorapophyllite-(NH4) is associated with calcite, tridymite, pyrite, chabazite-Ca and heulandite-Ca. It forms clusters, aggregates or crystalline crusts consisting of individual, well-developed crystals up to 4 mm in size, exhibiting the forms {110}, {101} and {001}. The mineral is colourless to light pink and translucent with white streak and vitreous to pearly lustre; it is non-fluorescent under ultraviolet radiation. The Mohs hardness is ~4½ to 5, tenacity is brittle, fracture is irregular, and there is perfect cleavage on {001}. The calculated density is 2.325 g cm–3. Fluorapophyllite-(NH4) is optically uniaxial (+) with ω = 1.5414(5) and ɛ = 1.5393(8) (λ = 589 nm). It is non-pleochroic. The empirical formula (based on 29 O + F apfu) is [(NH4)0.55K0.32Na0.07Ca0.06]Σ1.00(Ca4.01Mg0.02)Σ4.03Si7.97O20[F0.84(OH)0.16]Σ1.00⋅8H2O. Fluorapophyllite-(NH4) is tetragonal, space group P4/mnc, a = 8.99336(9) Å, c = 15.7910(3) Å, V = 1277.18(3) Å3 and Z = 2. The seven strongest X-ray powder diffraction lines are [dobs in Å,(I,%)(hkl)]: 7.897(32)(002), 7.812(13)(101), 4.547(14)(103), 3.946(100)(004), 2.985(39)(105), 2.4841(11)(215) and 1.5788(12)(00.10). The crystal structure of fluorapophyllite-(NH4), refined to R1 = 0.0299 for 743 unique (I > 3σI) observed reflections, confirmed that the atomic arrangement is very similar to that of the other members of the apophyllite group. The new mineral is named according to the current nomenclature scheme for apophyllite-group minerals and is an NH4 dominant analogue of fluorapophyllite-(K), fluorapophyllite-(Na) and fluorapophyllite-(Cs).

Chongite, Ca3Mg2(AsO4)2(AsO3OH)2·4H2O, a new arsenate member of the hureaulite group from the Torrecillas mine, Iquique Province, Chile

2016 ◽  
Vol 80 (7) ◽  
pp. 1255-1263 ◽  
Author(s):  
Anthony R. Kampf ◽  
Barbara P. Nash ◽  
Maurizio Dini ◽  
Arturo A. Molina Donoso
Keyword(s):  
Room Temperature ◽  
Obtuse Angle ◽  
New Mineral ◽  
Optical Orientation ◽  
X Ray Diffraction ◽  
Calculated Density ◽  
Secondary Alteration ◽  
X Ray ◽  
Mohs Hardness ◽  
Measured Density

AbstractThe new mineral chongite (IMA2015–039), Ca3Mg2(AsO4)2(AsO3OH)2.4H2O, was found at the Torrecillas mine, Iquique Province, Chile, where it occurs as a secondary alteration phase in association with native arsenic, arsenolite, gajardoite, talmessite and torrecillasite. Chongite occurs as prismatic crystals up to ∼1 mm long grouped in tightly intergrown radial aggregates up to 2 mm in diameter. Crystals are transparent, with vitreous lustre and white streak. The Mohs hardness is∼3½,tenacity is brittle and fracture is conchoidal. Cleavage is good on ﹛100﹜. The measured density is 3.09(2) g/cm3and the calculated density is 3.087 g/cm3. Optically, chongite is biaxial (-) with α = 1.612(1), β= 1.626(1), γ= 1.635(1) and 2V = 76.9(1)° (measured in white light). Dispersion isr < v,distinct. The optical orientation isX= b;Z^a =27° in obtuse angle β. The mineral is slowly soluble in dilute HCl at room temperature. The empirical formula, determined from electron-microprobe analyses, is (Ca2.90Mg1.93Mn0.14)Σ4.97As4O20H10.07. Chongite is monoclinic,die, a =18.5879(6),b =9.3660(3),c =9.9622(7) Å, β = 96.916(7)°,V=1721.75(14) Å3and Z=4. The eight strongest powder X-ray diffraction lines are[dobsÅ(I)(hkl)]: 8.35(29)(110), 4.644(62) (3ˉ11,020,400,2̄02), 4.396(26)(311), 3.372(62)(022,312,5̄11), 3.275(100)(420,22ˉ2,421), 3.113(57)(222), 2.384(30)(711,530,7̄12) and 1.7990(22)(9̄13,334,5̄34). The structure determination(R1= 1.56% for 1849 Fo> 4σFreflections) confirms that chongite is a member of the hureaulite group.

Štěpite, U(AsO3OH)2·4H2O, from Jáchymov, Czech Republic: the first natural arsenate of tetravalent uranium

2013 ◽  
Vol 77 (1) ◽  
pp. 137-152 ◽  
Author(s):  
J. Plášil ◽  
K. Fejfarová ◽  
J. Hloušek ◽  
R. Škoda ◽  
M. Novák ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Czech Republic ◽  
Uranium Atom ◽  
Short Wave ◽  
New Mineral ◽  
Oh Groups ◽  
X Ray ◽  
Tetravalent Uranium ◽  
Mohs Hardness ◽  
Oxygen Atoms

AbstractŠtěpite, tetragonal U(AsO3 OH)2(H2O)4 (IMA 2012-006), is the first natural arsenate of tetravalent uranium. It occurs in the Geschieber vein, Jáchymov ore district, Western Bohemia, Czech Republic, as emerald-green crystalline crusts on altered arsenic. Associated minerals include arsenolite, běhounekite, claudetite, gypsum, kaatialaite, the new mineral vysokýite (IMA 2012-067) and a partially characterized phase with the formula (H3O)+2(UO2)2(AsO4)2˙6H2O. Štěpite typically forms tabular crystals with prominent {001} and {010} faces, up to 0.6 mm in size. The crystals have a vitreous lustre and a grey to greenish grey streak. They are brittle with an uneven fracture and a very good cleavage on (001). Their Mohs hardness is about 2. Štěpite is not fluorescent in either short-wave or long-wave ultraviolet light. It is biaxial (–) with refractive indices (at 590 nm) of α = 1.636(2), β = 1.667(3), γ = 1.672(2) and 2Vobs < ~5°, anomalous greyish to pale yellow interference colours, and no pleochroism. The composition is as follows: 0.12Na2O, 50.19 UO2, 0.04SiO4, 0.09 P2O5, 0.93 As2O5, 1.95 SO3, 16.41 H2O; total 107.90 wt.%, yielding an empirical formula (based on 12 O a. p. f. u.) of (U1.01Na0.02)Σ1.03[(AsO3OH)1.82 (PO3OH)0.04(SO4)0.13(SiO4)0.01]Σ 2.00˙4H2O. Štěpite is tetragonal, crystallizing in space group I41/acd, with a = 10.9894(1), c = 32.9109(6) Å, V = 3974.5(1) Å3, Z = 16 and Dcalc = 3.90 g cm-3. The six strongest peaks in the X-ray powder-diffraction pattern [dobs in Å (I) (hkl)] are as follows: 8.190(100)(004), 7.008(43)(112), 5.475(18)(200), 4.111(16)(008), 3.395(20)(312,217), 2.1543(25)(419). The crystal structure of šteěpite has been solved from singlecrystal X-ray diffraction data by the charge-flipping method and refined to R1 = 0.0353 based on 1434 unique observed reflections, and to wR2 = 0.1488 for all 1523 unique reflections. The crystal structure of štšpite consists of sheets perpendicular to [001], made up of eight-coordinate uranium atoms and hydroxyarsenate 'tetrahedra'. The ligands surrounding the uranium atom consist of six oxygen atoms which belong to the hydroxyarsenate groups and two oxygen atoms which belong to interlayer H2 O molecules. Each UO8 polyhedron is connected to five other U polyhedra via six AsO3OH groups. Adjacent electroneutral sheets, of composition [U4+(AsO3OH)22-]0, are linked by hydrogen bonds involving H2 O molecules in the interlayers and OH groups in the sheets. The new mineral is named in honour of Josef Štěp (1863–1926), a Czech mining engineer and 'father' of the world's first radioactive spa at Jáchymov.

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