Crystalline Crusts Research Articles

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

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.

Investigation of plateau basin crustal structures and thickening mechanisms in the northeastern margin of the Tibetan plateau

This paper uses deep seismic sounding (DSS) data to contrast and analyze the crustal structures of three plateau basins (Songpan-Garze, Qaidam, Longzhong) in the northeastern margin of the Qinghai-Xizang (Tibetan) plateau, as well as two stable cratonic basins (Ordos, Sichuan) in its peripheral areas. Plateau basin crustal structures, lithological variations and crustal thickening mechanisms were investigated. The results show that, compared to the peripheral stable cratonic basins, the crystalline crusts of plateau basins in the northeastern margin are up to 10–15 km thicker, and the relative medium velocity difference is about 5% less. The medium velocity change in crustal layers of plateau basin indicates that the upper crust undergoes brittle deformation, whereas the lower crust deforms plastically with low velocity. The middle crust shows a brittle-to-plastic transition zone in this region. Thickening in the lower crust (about 5–10 km), and rheological characteristics that show low-medium velocity (relatively reduced by 7%), suggest that crustal thickening mainly takes place in lower crust in the northeastern margin of the Tibetan plateau. The crust along the northeastern margin shows evidence of wholesale block movement, and crustal shortening and thickening seem to be the main deformation features of this region. The GPS data show that the block motion modes and crustal thickening in the Tibetan plateau is closely related to the peripheral tectonic stress field and motion direction of the Indian plate. The Mani-Yushu-Xianshuihe fold belt along the boundary between the Qiangtang block and the Bayan Har block divides the different plateau thickening tectonic environments into the middle-western plateau, the northeastern margin and the southeastern plateau.

Xocolatlite, Ca2Mn24+Te2O12{middle dot}H2O, a new tellurate related to kuranakhite: Description and measurement of Te oxidation state by XANES spectroscopy

Xocolatlite, Ca2Mn4+2 Te6+2O12·H2O, is a rare new mineral from the Moctezuma deposit in Sonora, Mexico. It occurs as chocolate-brown crystalline crusts on a quartz matrix. Xocolatlite has a copperbrown streak, vitreous luster, and is transparent. Individual crystals show a micaceous habit. Refractive indices were found to be higher than 2.0. Density calculated from the empirical formula is 4.97 g/cm3, and immersion in Clerici solution indicated a density higher than 4.1 g/cm3. The mineral is named after the word used by the Aztecs for chocolate, in reference to its brown color and provenance.

Hydraulic observations from a 1 year fluid production test in the 4000 m deep KTB pilot borehole

AbstractA long‐term pump test was conducted in the KTB pilot borehole (KTB‐VB), located in the Oberpfalz area, Germany. It produced 22 300 m3 of formation fluid. Initially, fluid production rate was 29 l min−1 for 4 months, but was then raised to an average of 57 l min−1 for eight more months. The aim of this study was to examine the fluid parameters and hydraulic properties of fractured, crystalline crusts as part of the new KTB programme ‘Energy and Fluid Transport in Continental Fault Systems’. KTB‐VB has an open‐hole section from 3850 to 4000 m depth that is in hydraulic contact with a prominent continental fault system in the area, called SE2. Salinity and temperature of the fluid inside the borehole, and consequently hydrostatic pressure, changed significantly throughout the test. Influence of these quantities on variations in fluid density had to be taken into account for interpretation of the pump test. Modelling of the pressure response related to the pumping was achieved assuming the validity of linear Darcy flow and permeability to be independent of the flow rate. Following the principle ‘minimum in model dimension’, we first examined whether the pressure response can be explained by an equivalent model where rock properties around the borehole are axially symmetric. Calculations show that the observed pressure data in KTB‐VB can in fact be reproduced through such a configuration. For the period of high pumping rate (57 l min−1) and the following recovery phase, the resulting parameters are 2.4 × 10−13 m3 in hydraulic transmissivity and 3.7 × 10−9 m Pa−1 in storativity for radial distances up to 187 m, and 4.7 × 10−14 m3 and 6.0 × 10−9 m Pa−1, respectively, for radial distances between 187 and 1200 m. The former pair of values mainly reflect the hydraulic properties of the fault zone SE2. For a more realistic hydraulic study on a greater scale, program FEFLOW was used. Parameter values were obtained by matching the calculated induced pressure signal to fluid‐level variations observed in the KTB main hole (KTB‐HB) located at 200 m radial distance from KTB‐VB. KTB‐HB is uncased from 9031 to 9100 m and shows indications of leakage in the casing at depths 5200–5600 m. Analysis of the pressure record and hydraulic modelling suggest the existence of a weak hydraulic communication between the two boreholes, probably at depths around the leakage. Hydraulic modelling of a major slug‐test in KTB‐HB that was run during the pumping in KTB‐VB reveals the effective transmissivity of the connected formation to be 1 to 2 orders of magnitude lower than the one determined for the SE2 fault zone.

The Paleocene travertine system of the Itaboraí basin, Southeastern Brazil

The record of pre-Quaternary travertines is restricted to relatively few publications in the geological literature. In this paper, the authors present a petrographic and geochemical study of Paleocene travertines partly exposed in the Itaboraí basin, a small half-graben of southeastern Brazil. Travertine lithofacies were defined mainly from borehole samples, and these data were integrated with available field information. The most representative lithofacies of the travertine system are crystalline crusts that developed around springs at the surface and close to the fault. Other lithofacies, such as pisoid, micritic, and lithoclast travertines and tufas, were deposited distally from the springs. Mn and Fe carried to the surface by rising waters were incorporated in CL-zoned fibrous calcite and precipitated as iron-bearing minerals, respectively. Both goethite in the crystalline crusts and pyrite in the micritic travertine probably formed under biotic mediation. The evolution of this travertine system was related to Cenozoic reactivation of a shear zone in the Precambrian basement at the southern border of the basin. 87Sr/ 86Sr ratios indicate that groundwaters interacted with subsurface Precambrian marbles and gneisses before reaching the surface. δ 13C and δ 18O data suggest that several factors influenced carbonate precipitation in distal settings and that crystalline crusts formed from waters that changed in composition in the spring outlets and/or downflow within the travertine system.

Rapid facies changes in Holocene fissure ridge hot spring travertines, Rapolano Terme, Italy

Holocene hot water travertine continues to form at Terme San Giovanni, near Rapolano Terme, central Italy, although artificial diversion of the water has reduced deposition. Mesothermal water (≈38–39 °C) emerging from fault‐controlled vents located on a hilltop has created a linear fissure ridge 240 m long and up to 10 m high. Active parts of the ridge crest are covered by small cones; inactive parts are locally neotectonically fissured and have small pools. Ridge deposits include crystalline crust, paper‐thin raft and shrub lithotypes. The ridge has both smooth and terraced marginal slopes, dominated by crystalline crusts with small shrubs in terrace pools. At the base of the ridge, there is a rapid transition to lateral flats and depressions, where water from the ridge collects and deposits shrub, irregular pisoid, reed, paper‐thin raft and fine‐grained and organic‐rich travertines. Water channelled to nearby valley sides deposits thick crystalline crusts on valley slopes and waterfall overhangs, locally with small pools filled by smooth spherical pisoids. On the valley floor, mixing of waters forms varied stream‐fill deposits that include micritic reed, paper‐thin raft and coated bubble travertines. The diversity of travertine facies observed results from the location of the Terme San Giovanni hot springs on a hill crest, thus providing a wide array of downslope locations for further deposition. The abrupt facies transitions observed are characteristic of hot spring carbonates and result from a combination of rapid decrease in precipitation away from vents, variations in local surface topography and the feedback effect of travertine deposition itself, which dams and diverts water flow.

Hot‐spring travertine facies and sequences, Late Pleistocene, Rapolano Terme, Italy

Late Pleistocene travertines up to 40 m thick near Rapolano Terme in Tuscany, central Italy, were precipitated by hot water issuing from springs on hillsides and flowing into adjacent depressions to mix with rainwater. Proximal light‐coloured slope and terrace travertines pass distally into darker reed mound and depression‐fill travertines. Lithotypes include crystalline crust, shrub, pisoid, paper‐thin raft, coated bubble, reed, and lithoclast‐breccia. High precipitation rates resulted in rapid slope aggradation and progradation. Dilution by rainwater likely lowered precipitation rates in depressions, but deposition was augmented by allochthonous material eroded from upslope travertines.Slope Depositional Systems consist of Smooth and Terrace Slope facies characterized by white crystalline crusts, with diverse additional lithotypes in terrace pools. Depression Depositional Systems have mixed light and dark travertines with horizontal to gently concave stratification. Extensive light‐coloured Shrub Flat travertine is dominant; darker Marsh‐Pool Facies composed of fine lithoclast and reed travertine is localized. Reed Mounds composed of mixed light and dark travertines localized by abundant reed growth, formed where spring water emerged near the bases of low angle slopes.Distal reduction in accretion rate was the major influence on sequence development. Light‐coloured slope travertines interdigitate with darker depression deposits. Vertical aggradation of slope deposits, mound progradation, and filling of topographic depressions is expressed by advance and retreat of facies. Evolution from depression to slope or mound sequences is termed ‘steepening up’. Up‐sequence change from slope or mound to depression facies is termed ‘levelling up’. Exposure surfaces associated with palaeosols are common in all facies and often constitute sequence boundaries. They are more closely spaced in depression sequences, reflecting slower and possibly also more discontinuous accumulation at sites furthest from hot springs.

Possible microbial effects of stable carbon isotopes in hot-spring travertines

Recent and older (early Holocene to Pleistocene) hot-spring travertine carbonates from central Italy have two distinctive macrofabrics, crystalline crusts and shrubs. Crystalline crusts are laminated slope deposits that formed abiotically following CO 2 degassing from spring water. The formation of shrub travertine--irregular, dendritic precipitates from pool environments--is controversial and has been attributed to both abiotic and microbial processes. Oxygen isotope variation in our travertines can be explained by abiotic processes, mainly CO 2 degassing. In contrast, our carbon isotope data cannot be wholly explained by abiotic CO 2 degassing invoked in earlier studies. Because photosynthesis is known to preferentially remove 12 C, leaving ambient waters enriched in 13 C, this fractionation should be recorded in delta 13 C values of microbially influenced travertine. Our shrub carbon isotope values are between 0.5 per thousand and 6.0 per thousand larger than values for associated abiotic precipitates, and this difference is probably caused by microbial activity. These isotope data support previous visual evidence that some shrub fabrics are microbially influenced.

Les phosphates d'uranyle et d'aluminium de Kobokobo. II. La phuralumite Al2 (UO2)3 (PO4)2 (OH)6 • 10H2O et l'upalite Al (UO2)3 (PO4)2 (OH)3, nouveaux minéraux

Phuralumite occurs as yellow lemon prismatic crystals. Perfect vertical cleavage {010}. Maximum length 1/2 mm. Density (measured) 3.5 g/cm3. Optically biaxial negative, 2V = 40° ; ng (pale yellow) = 1.624, nm (pale yellow) = 1.616 and np (bright yellow) = 1.559. Phuralumite is monoclinic, P21/a with a = 13.87 Å, b = 20.79 Å, c = 9.38 Å and β = 112° ; Z = 4 ; d(calc) = 3.54 g/cm3. The strongest lines of the X-ray powder pattern are : 10.4 Å (100) 020, 3.08 Å (80) 202-213-422, 5.17 Å (70) 040 and 3.40 Å (50) 242. Formula deduced from electron microprobe analysis (H2O by difference) : Al2 (UO2)3(PO4)2(OH)6-10H2O. Upalite occurs as acicular prisms. Colour : amber yellow, transparent. Maximum length : 1/3 mm. Cleavage {010} distinct. Density (measured) 3.5 g/cm3. The mineral is orthorhombic ; space group Bbcm or Bba2 with a = 34.68 Å , b = 16.81 Å and c = 13.72 Å. Z = 16. Calculated density 3.58 g/cm3. The strongest lines of the X-ray powder pattern are : 8.4 Å (100) 020, 4.18 Å (80) 040, 3.43 Å (80) 004 and 2.903 Å (75) 10.2.2. Upalite is biaxial, 2 V(—) = 74° ; ng (canary yellow) = 1.676, nm (canary yellow) = 1.666 and np (colourless) = 1.649. Formula from microprobe analysis (H2O by difference) : Al (UO2)3 (OP4)2 (OH)3. Structural group of phosphuranylite, as well as phuralumite. Both minerals occur at Kobokobo, Kivu, Zaïre, as crystalline crusts and veinlets on pegmatitic rocks. The names after the chemical composition.

Crystal Textures of Recent Fluvial Pisolites and Laminated Crystalline Crusts in Dyfed, South Wales

ABSTRACT Pisoliths, rimstone pools, and laminated crystalline crusts are described from Dyfed, South Wales, which resemble cave pearls and stalagmitic deposits but are formed in streams on an open hillside. The crystalline deposits are entirely calcite and share a common petrographic character. Crystals may be divided into three groups: 1) acicular fibres, which form radial or spherular clusters defining a succession of botryoidal surfaces 2) prismatic crystals, with rhomboidal terminations which become rounded or flattened by solution at right angles to their axes and 3) prismatic crystals, with ragged boundaries formed by the lateral coalescence of fibrous or prismatic elements separated by low-angle tilt boundaries. The latter contain linear inclusions which are relicts of their fibrous precursors. Associated sediments include plant fragments (principally Polytrichum) and gastropods (Oxychilus) crusted with radial crystalline fringes, but are of two main kinds: 1) poorly sorted aggregated and peloidal micrites which contain a variety of lithoclasts and 2) crystal cumulates formed by the mechanical breakdown and re-sedimentation of the crystals described above. The form of the crystals is related to the presence of foreign ions in solution. The external morphology of the deposits is controlled by the rate of flow and the depth of water films. Pisoliths do not require continuous agitation.

Facies, Diagenesis, and Porosity Development in Lower Cretaceous Bank Complex, Edwards Limestone, North-Central Texas: ABSTRACT

An Edwards carbonate bank complex developed on the structurally positive Belton high in north central Texas. Mobile carbonate sand bars, rudist reefs, and beaches of the shallow-water bank differ strikingly from time-equivalent deeper water muds of the Tyler basin to the north, and supratidal dolomites and evaporites of the central Texas platform to the south. Early stages of bank development are well-exposed near Belton, Texas, and exhibit the following progradational vertical facies succession: open marine basin, shallow grain shoal, rudist path reef, exposed beach, restricted lagoon, and intertidal-supratidal mud flats. Paleocaliche, desiccation cracks, and algal boundstone suggest subaerial exposure of the uppermost unit. The major diagenetic changes occurred early, and predate regional exposure of the bank complex at the end of Edwards time. Most calcite cementation is early, and associated with local meteoric water tables, where fine crystalline bladed crusts, syntaxial overgrowths, solution-cavity fill, and medium to coarse crystalline equant calcite were precipitated. Early Mg-calcite bladed crusts also formed in the marine or mixing zone environments. Late-stage calcite cementation was limited to coarse crystalline equant calcite. Most of the dolomite is of multi-stage fresh water mixing origin. Dolomitization of lime muds and calcite cements occurred early, in association with local meteoric water tables, and late, as the result of a meteoric ground water system. Fine crystalline anhedral dolomite in lagoonal and tidal flat facies is of hypersaline origin. The shoreface and foreshore facies of the beach complex have up to 35 percent (thin section estimated) moldic and interparticle porosity as a result of (1) high original interparticle porosity, (2) early cementation to reduce compaction, (3) aragonite allochem dissolution to produce moldic porosity, (4) subaerial exposure to reduce further cementation, and (5) an early seal to retard fluid migration. The lagoonal and tidal flat facies have up to 20 percent (estimated) moldic and intercrystalline porosity due to (1) dissolution of aragonitic allochems, and (2) partial dolomitization and subsequent dissolution of the lime mud. 'Shell Oil Company, Houston, Texas HYDROGEN AND OXYGEN ISOTOPIC COMPOSITION OF CHERT FROM THE EDWARDS GROUP, LOWER CRETACEOUS, CENTRAL TEXAS

Guano minerals from Murra-el-elevyn Cave Western Australia

Summary Biphosphammite, ammonian KH2PO4, syngenite, aphthitalite, monetite, hannayite, whitloekite, apatite and minor gypsum, taylorite, brushite, mirabilite, guanine, and unidentified compounds form crystalline crusts on the walls and floors of a chamber of Murra-el-elevyn Cave, Cocklebiddy, Nullarbor Plain, Western Australia. The minerals are derived from the interaction of bat urine, droppings, and limestone. Analyses for CaO, MgO, Na2O, K2O, SO3, P2O5, CO2, NH3, H2O-, total N, and ignition loss are given. High K2O and low total N figures are characteristic of the analyses.

VIII.—On the Association of Stibnite and Cinnabar in Mineral Deposits

The association of stibnite and cinnabar appears to have been first noticed at El Haminat, in the province of Constantine Algiers, where, during the years 1850 to 1852, considerable quantities of both these minerals have been raised from veins traversing Cretaceous schists. Other localities in Algiers showing the same association are: Ghelma near Phillipsville, where cinnabar in crystalline crusts covers and penetrates antimony ochre derived from the decomposition of stibnite, the containing rock being a saccharoidal limestone; Debar, 19 kilometers to the N.W. of Ghelma, where stibnite is found covered with spots of cinnabar, the gangue being heavy spar; Traia, showing a similar occurrence to the preceding; Tasselemet, where radiating crystals of stibnite occur imbedded in earthy cinnabar.