ALBERT

Description: Stepite, tetragonal U(AsO 3 OH) 2 (H 2 O) 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, behounekite, claudetite, gypsum, kaatialaite, the new mineral vysokyite (IMA 2012-067) and a partially characterized phase with the formula $${\left({\mathrm{H}}_{3}\mathrm{O}\right)}_{2}^{+}$$ (UO 2 ) 2 (AsO 4 ) 2 ·6H 2 O. Stepite 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. Stepite 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), = 1.672(2) and 2V obs 〈 ~5°, anomalous greyish to pale yellow interference colours, and no pleochroism. The composition is as follows: 0.12 Na 2 O, 50.19 UO 2 , 0.04 SiO 4 , 0.09 P 2 O 5 , 0.93 As 2 O 5 , 1.95 SO 3 , 16.41 H 2 O; total 107.90 wt.%, yielding an empirical formula (based on 12 O a.p.f.u.) of (U 1.01 Na 0.02 ) 1.03 [(AsO 3 OH) 1.82 (PO 3 OH) 0.04 (SO 4 ) 0.13 (SiO 4 ) 0.01 ] 2.00 ·4H 2 O. Stepite is tetragonal, crystallizing in space group I 4 1 / acd , with a = 10.9894(1), c = 32.9109(6) Å, V = 3974.5(1) Å 3 , Z = 16 and D calc = 3.90 g cm –3 . The six strongest peaks in the X-ray powder-diffraction pattern [ d obs 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 stepite has been solved from single-crystal X-ray diffraction data by the charge-flipping method and refined to R 1 = 0.0353 based on 1434 unique observed reflections, and to wR 2 = 0.1488 for all 1523 unique reflections. The crystal structure of stepite 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 H 2 O molecules. Each UO 8 polyhedron is connected to five other U polyhedra via six AsO 3 OH groups. Adjacent electroneutral sheets, of composition $${\left[{\mathrm{U}}^{4+}{\left({\mathrm{AsO}}_{3}\mathrm{OH}\right)}_{2}^{2-}\right]}^{0}$$ , are linked by hydrogen bonds involving H 2 O molecules in the interlayers and OH groups in the sheets. The new mineral is named in honour of Josef Step (1863–1926), a Czech mining engineer and ‘father’ of the world's first radioactive spa at Jáchymov.

Description: Two crystals of the uranyl carbonate mineral grimselite, ideally K3Na[(UO2)(CO3)3](H2O), from Jáchymov in the Czech Republic were studied by single-crystal X-ray diffraction and electron-probe microanalysis. One crystal has considerably more Na than the ideal chemical composition due to substitution of Na into KO8 polyhedra; the composition of the other crystal is nearer to ideal, and similar to synthetic grimselite. The presence of Na atoms in KO8 polyhedra, which are located in channels in the crystal structure, reduces their volume, and as a result the unit-cell volume also decreases. Structure refinement shows that the formula for the sample with the anomalously high Na content is (K2.43Na0.57)Σ3.00Na[(UO2)(CO3)3](H2O). The unit-cell parameters, refined in space group P6İ2c, are a = 9.2507(1), c = 8.1788(1) Å, V = 606.14(3) Å3 and Z = 2. The crystal structure was refined to R1 = 0.0082 and wR1 = 0.0185 with a GOF = 1.33, based on 626 observed diffraction peaks [Iobs〉3σ(I)].

Description: Behounekite, orthorhombic U(SO4)2(H2O)4, is the first natural sulphate of U4+. It was found in the Geschieber vein, Jáchymov (St Joachimsthal) ore district, Western Bohemia, Czech Republic, crystallized on the altered surface of arsenic and associated with kaatialaite, arsenolite, claudetite, unnamed phase UM1997-20-AsO:HU and gypsum. Behounekite most commonly forms short-prismatic to tabular green crystals, rarely up to 0.5 mm long. The crystals have a strong vitreous lustre and a grey to greenish grey streak. They are brittle with an uneven fracture and have very good cleavage along {100}. The Mohs hardness is about 2. The mineral is not fluorescent either in short- or long-wavelength UV radiation. Behounekite is moderately pleochroic, a~ß is pale emerald green and ? is emerald green, and is optically biaxial (+) with a = 1.590(2), ß = 1.618(4), ? = 1.659(2) (590 nm), 2V (calc.) = 81°, birefringence 0.069. The empirical formula of behounekite (based on 12 O atoms, from an average of five point analyses) is (U0.99Y0.03)S1.02(SO4)1.97(H2O)4. The simplified formula is U(SO4)2(H2O)4, which requires UO2 53.77, SO3 31.88, H2O 14.35, total 100.00 wt.%. Behounekite is orthorhombic, space group Pnma, a = 14.6464(3), b = 11.0786(3), c = 5.6910(14) Å, V = 923.43(4) Å3, Z = 4, Dcalc = 3.62 g cm-3. The seven strongest diffraction peaks in the X-ray powder diffraction pattern are [dobs in Å (I) (hkl)]: 7.330 (100) (200), 6.112 (54) (210), 5.538 (21) (020), 4.787 (42) (111), 3.663 (17) (400), 3.478 (20) (410), 3.080 (41) (321). The crystal structure of behounekite has been solved by the charge-flipping method from single-crystal X-ray diffraction data and refined to R1 = 2.10 % with a GOF = 1.51, based on 912 unique observed diffractions. The crystal structure consists of layers built up from [8]-coordinate uranium atoms and sulphate tetrahedra. The eight ligands include four oxygen atoms from the sulphate groups and four oxygen atoms from the H2O molecules. Each uranium coordination polyhedron is connected via sulphate tetrahedra with other uranium polyhedra and through hydrogen bonds to the apices of sulphate tetrahedra. The dominant features of the Raman and infrared spectra of behounekite are related to stretching vibrations of SO4 tetrahedra (~1200–950 cm-1), O–H stretching modes (~3400–3000 cm-1) and H–O–H bending modes (~1650 cm-1). The mineral is named in honour of František Behounek, a well known Czech nuclear physicist.

Description: The crystal structure of pseudojohannite from White Canyon, Utah, was solved by charge-flipping from single-crystal X-ray diffraction data and refined to an R obs = 0.0347, based on 2664 observed reflections. Pseudojohannite from White Canyon is triclinic, P , with a = 8.6744(4), b = 8.8692(4), c = 10.0090(5) Å, α = 72.105(4)°, β = 70.544(4)°, = 76.035(4)°, and V = 682.61(5) Å 3 , with Z = 1 and chemical formula Cu 3 (OH) 2 [(UO 2 ) 4 O 4 (SO 4 ) 2 ](H 2 O) 12 . The crystal structure of pseudojohannite is built up from sheets of zippeite topology that do not contain any OH groups; these sheets are identical to those found in zippeites containing Mg 2+ , Co 2+ , and Zn 2+ . The two Cu 2+ sites in pseudojohannite are [5]- and [6]-coordinated by H 2 O molecules and OH groups. The crystal structure of the pseudojohannite holotype specimen from Jáchymov was refined using Rietveld refinement of high-resolution powder diffraction data. Results indicate that the crystal structures of pseudojohannite from White Canyon and Jáchymov are identical.

Description: The crystal structure of deliensite, Fe[(UO 2 ) 2 (SO 4 ) 2 (OH) 2 ](H 2 O) 7 , was solved by direct methods and refined to R 1 = 6.24% for 5211 unique observed reflections [ I obs 〉 3( I )], on a crystal that was found to consist of rotational and inversion (merohedral) twins, from Jeronym mine, Abertamy in the Czech Republic. The presence of four twin domains was taken into account in the refinement. The structure is orthorhombic, space group Pnn2 , with unit-cell parameters a = 15.8514(9), b = 16.2478(7), c = 6.8943(3) Å, V = 1775.6(1) Å 3 and Z = 4. The crystal structure of deliensite contains uranyl-sulfate sheets with a phosphuranylite topology, consisting of dimers of edge-sharing uranyl pentagonal bipyramids linked by corner-sharing with sulfate tetrahedra. The sheets lie in the (100) plane and are decorated by [Fe 2+ O(H 2 O) 5 ] octahedra; two weakly bonded H 2 O molecules are present in the interlayer. The [Fe 2+ O(H 2 O) 5 ] octahedron is linked directly to the sheet via the uranyl oxygen atom. Adjacent sheets are linked by hydrogen bonds only. The sheet topology and geometrical isomerism is discussed and a comparison of the composition obtained from electron-probe microanalysis, powder-diffraction data, Raman and infrared spectra of deliensite samples from Mas d'Alary, Lodève, France; L'Ecarpière mine, Gétigné, France; and several localities at Jáchymov, Western Bohemia, Czech Republic is made.

Description: Svenekite (IMA 99-007), Ca[AsO 2 (OH) 2 ] 2 , is a rare supergene arsenate mineral occurring in the Geschieber vein, Jáchymov ore district, Western Bohemia, Czech Republic. It grows directly on the granite rocks and occurs isolated from other arsenate minerals otherwise common in Jáchymov. Svenekite usually forms clear transparent coatings composed of indistinct radiating to rosette-shaped aggregates up to 3 mm across. They are composed of thin lens- or bladed-shaped crystals, usually 100–150 μm long.Svenekite is transparent to translucent and has a white streak and a vitreous lustre; it does not fluoresce under ultraviolet light. Cleavage is very good on {010}. The Mohs hardness is ~2. Svenekite is biaxial, non-pleochroic. The refractive indices are α' = 1.602(2), ' = 1.658(2). The empirical formula ofsvenekite (based on As + P + S = 2 a.p.f.u., an average of 10 spot analyses) is (Ca 1.00 Mg 0.01 ) 1.01 [AsO 2 (OH) 2 ] 1.96 [PO 2 (OH) 2 ] 0.03 (SO 4 ) 0.01 . The simplified formula is Ca[AsO 2 (OH) 2 ] 2 and requires CaO 17.42, As 2 O 5 71.39, H 2 O 11.19, total 100.00 wt.%. Raman and infrared spectroscopy exhibit dominance of O–H vibrations and vibration modes of distorted tetrahedral AsO 2 (OH) 2 units.Svenekite is triclinic, space group P 1I, with a = 8.5606(5), b = 7.6926(6), c = 5.7206(4) Å , α = 92.605(6), β = 109.9002(6), = 109.9017(6)°, and V = 327.48(4) Å 3 , Z = 2, D calc = 3.26 g·cm –3 . The a:b:c ratio is 0.7436:1:1.1082 (for single-crystal data). The six strongest diffraction peaks in the X-ray powder diffraction pattern are [ d ( Å)/ I (%)/( hkl )]: 3.968(33)(21I0); 3.766(35)(21I1I); 3.697(49)(101); 3.554(100)(020); 3.259(33)(22I0); 3.097(49)(12I1). The crystal structure of svenekite was refined from single-crystal X-ray diffraction data to R 1 = 0.0250 based on 1309 unique observed, and to wR 2 = 0.0588, for all 1588 unique reflections (with GOF all = 1.20). The structure of svenekite consists of sheets of corner-sharing CaO 8 polyhedra and AsO 2 OH 2 groups, stacked parallel to (001). Adjacent sheets are linked by hydrogen bonds. Thesvenekite structure possesses very short symmetrical hydrogen bonds (with the D –H lengths ~1.22 Å). The mineral is named to honour JaroslavSvenek, the former curator of the mineralogical collection of the National Museum in Prague, Czech Republic.

Description: Vysokyite, U 4+ [(AsO 2 (OH) 2 ] 4 (H 2 O) 4 (IMA 2012–067), was found growing on an altered surface of massive native As in the Geschieber vein, Jáchymov ore district, Western Bohemia, Czech Republic. The new mineral was found in association with behounekite, stepite, kaatialaite, arsenolite, claudetite and gypsum. It forms extremely fibrous light-green crystals up to 8 mm long. Crystals have an alabaster lustre and a greenish-white to greyish streak. Vysokyite is brittle with uneven fracture and perfect cleavage along (100) and (001); the Mohs hardness is ~2. A density of 3.393 g/cm 3 was calculated using the empirical formula and unit-cell parameters obtained from a single-crystal diffraction experiment. Vysokyite is non-fluorescent under short or long wavelength UV radiation. It is colourless under the microscope, measured refractive indices are α' = 1.617(3), ' = 1.654(3); the estimated optical orientation is α' ~ X , ' ~ Z . The average of five spot wavelength dispersive spectroscopy (WDS) analyses is 29.44 UO 2 , 1.03 SiO 2 , 48.95 As 2 O 5 , 0.12 SO 3 , 15.88 H 2 O (calc.), total 95.42 wt.%. The empirical formula of vysokyite (based on 20 O a.p.f.u.) is U 1.00 [AsO 2 (OH) 2 ] 3.90 (SiO 4 ) 0.16 (SO 4 ) 0.01 ·4H 2 O. The As–O–H and O–H vibrations dominate in the Raman spectrum. Vysokyite is triclinic, space group P 1I, with a = 10.749(2), b = 5.044(3), c = 19.1778(7) Å, α = 89.872(15)°, β = 121.534(15)°, = 76.508(15)°, and V = 852.1(6) Å 3 , Z = 2 and D calc = 3.34 g·cm –3 . The strongest diffraction peaks in the X-ray powder diffraction pattern are [ d obs in Å( I rel. )( hkl )]: 8.872(100)(100), 8.067(50)(002), 6.399(7)(103I), 4.773(6)(104I), 3.411(10)(302I), 3.197(18)(313I). The crystal structure of vysokyite was solved from single-crystal X-ray diffraction data by the charge-flipping method and refined to R 1 = 0.0595 based on 2718 unique observed reflection, and to wR 2 = 0.1160 for all 4173 unique reflections. The structure of vysokyite consists of UO 8 square antiprisms sharing all of their vertices with 8 As-tetrahedra to form infinite chains parallel to [010]. These chains are linked by hydrogen bonds involving terminal (OH) groups of the double-protonated As-tetrahedra and molecules of H 2 O located between the chains. The new mineral is named in honour of Arnost Vysoky (1823–1872), the former chief of the Jáchymov mines and smelters, chemist and metallurgist.