Paulscherrerite

Last updated
Paulscherrerite
General
Category Oxide minerals,
uranyl hydroxides
Formula
(repeating unit)		UO2(OH)2
IMA symbol Psc [1]
Strunz classification 4.GA.05
Crystal system Monoclinic
Unknown space group
Identification
ColorCanary yellow
Crystal habit Microcrystalline powder
Cleavage Undetermined
Fracture Undetermined
Mohs scale hardnessUndetermined
Streak Yellow
Specific gravity 6.66 g/cm3
Ultraviolet fluorescence none
Other characteristics Radioactive.svg Radioactive
References [2] [3]

Paulscherrerite, UO2(OH)2, is a newly named mineral of the schoepite subgroup of hexavalent uranium hydrate/hydroxides. It is monoclinic, but no space group has been determined because no single-crystal study has been done. Paulscherrerite occurs as a canary yellow microcrystalline powdery product with a length of ~500 nm. It forms by the weathering and ultimate pseudomorphism of uranium-lead bearing minerals such as metaschoepite. The type locality for paulscherrerite is the Number 2 Workings, Radium Ridge near Mount Painter, North Flinders Ranges, South Australia, an area where radiogenic heat has driven hydrothermal activity for millions of years. It is named for Swiss physicist Paul Scherrer, co-inventor of the Debye-Scherrer X-ray powder diffraction camera. Study of paulscherrerite and related minerals is important for understanding the mobility of uranium around mining sites, as well as designing successful strategies for the storage of nuclear weapons and the containment of nuclear waste.

Contents

Introduction

The schoepite subgroup of the fourmarierite group: schoepite, metaschoepite, paraschoepite, and "dehydrated schoepite", are closely related hexavalent uranium (uranyl) oxide hydrates/hydroxides. [4] Schoepite was first described by T. L. Walker in 1923 and the determination of the relationship between the various subgroups has since been ongoing. Detailed X-ray powder diffraction and single crystal studies have led to a better understanding of the natural dehydration process of schoepite that result in the rest of the subgroup. [5] "Dehydrated schoepite" has now been formally described as a mineral species by a team of geologists led by Joel Brugger of the University of Adelaide, Australia and given the name paulscherrerite, with the formula UO3·1.02H2O.

Composition

The empirical formula for paulscherrerite is UO3·1.02H2O. The formulas for the rest of the schoepite group are: schoepite (UO2)8O2(OH)12 · 12H2O and metaschoepite UO3·1-2H2O. Electron microprobe 20 point analyses showed that it is an almost pure uranyl oxide-hydroxide/hydrate, with less than ~1 wt% of minor elements such as Al, Ba, and Pb. The simplified structural formula is UO2(OH)2, which requires the presence of water: UO3 93.96, H2O 6.04, Total 100.00 wt%. Table 1 shows an analysis of the chemical composition. Because paulscherrerite always exists in powder form, mixed with substantial amounts of metaschoepite, thermogravimetric analysis (TGA) is the best method of water measurement. [6]

Structure

Paulscherrerite is monoclinic (pseudo-orthrombic), with a = 4.288(2), b = 10.270(6), c = 6.885(5)Å, β = 90.39(4) = 90.39(4)o, V = 303.2(2)Å3, and Z = 4. No space group determination has been made, as no single-crystal study has been done. Given the very small crystallites (less than a few tens of nanometers), it is very difficult to distinguish an orthorhombic cell from a monoclinic cell with β close to 90° (Bevan et al. 2002). Possible space groups that explain all 46 reflections found include: P2, P21, P2/m, and P21/m. The structures of the closely related schoepite, [7] metaschoepite [8] consist of layers formed by edge-sharing UO7 pentagonal bi-pyramids interspersed with hydrogen bounded water molecules. The structure of orthorhombic α-UO2(OH)2 (synthesized "dehydrated schoepite"), however, consists of layers formed by edge sharing UO8 hexagonal bipyramids. [9] The uranyl sheets in schoepite/metaschoepite and α-UO2(OH)2 are topologically related via the substitution 2(OH) = O2 + vacancy. [6]

Physical properties

Paulscherrerite occurs as a microcrystalline powdery product with a maximum length of ~500 nm. It forms by the weathering and ultimate pseudomorphism of uranium-lead bearing minerals such as metaschoepite. [6] Paulscherrerite is canary yellow, with a yellow streak, and no fluorescence. The Mohs hardness cannot be measured due to the powdery nature of the mineral, and no cleavage or fracture is observable. The calculated density is 6.66 g/cm3 for the ideal formula UO2(OH)2. No optical properties have been recorded. See Table 1 for a list of the physical properties of paulscherrerite.

Geologic occurrence

The type locality for paulscherrerite is the Number 2 Workings, Radium Ridge near Mount Painter, North Flinders Ranges, South Australia, which contains large volumes of granites and gneisses highly enriched in uranium and thorium. The Number 2 Workings expose a lens of massive coarse-grained hematite with a fine-grained monazite-(Ce), xenotime-(Y), and Ca-Fe-phosphate matrix and abundant iron-rich euxenite. [6] The radiogenic heat produced by uranium-thorium-potassium-rich rocks drove hydrothermal activity over hundreds of millions of years. [10] These conditions of high-temperature hydrothermal mineralization are ideal for the formation and deposition of abundant deposits of paulscherrerite, a dehydration product of metaschoepite. Secondary uranium minerals occur in cavities of the predominant hematite/quartz including weeksite, beta-uranophane, metatorbernite, soddyite, kasolite, billietite, and barite. [11] Figure 3. shows the geomorphology of the Mt. Gee – Mt. Painter epithermal system. “Dehydrated-schoepite” has also been identified as an early product of uraninite weathering in the Ruggles and Palermo granitic pegmatites, New Hampshire, U.S. [12]

Special characteristics

Schoepite, metaschoepite, and paulscherrerite result from the weathering of uranium minerals such as uraninite and the corrosion of anthropogenic uranium bearing solids. [13] The oxy-hydroxides of the shoepite subgroup act as precursors in the formation of more complex and stable assemblages (Brugger et al. 2003). Study of these minerals is important for understanding the mobility of uranium around mining sites, as well as designing successful strategies for the storage of nuclear weapons and the containment of nuclear waste.

Biographic sketch

Paulscherrerite is named in recognition of the vital contributions to mineralogy and nuclear physics of Swiss physicist Paul Scherrer (1890–1969). While studying at the University of Göttingen in 1916, he and Peter Debye, Scherrer's mentor and eventual Nobel Prize winner, developed the powder diffraction theory (the Scherrer equation) and designed the Debye-Scherrer X-ray powder diffraction camera. [6] By 1920, Scherrer had become interested in nuclear physics, was appointed to a professorship at the ETH Zürich, and was involved in the early development of solid-state physics, nuclear physics, and electronics. He was named President of the Swiss Study Commission for Atomic Energy in 1946 and took part in establishing CERN near Geneva in 1954 (Hephaestus, 2011). Since 1988, the Paul Scherrer Institute has been the largest Swiss national research institute, active in elementary particle physics, material sciences, and nuclear and non-nuclear energy research. The name for the mineral was proposed by Joel Brugger, a native of Switzerland, currently a QEII fellow at the University of Adelaide, Australia (MMSN, 2011).

See also

Related Research Articles

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<span class="mw-page-title-main">Yellowcake</span> Uranium concentrate powder

Yellowcake is a type of uranium concentrate powder obtained from leach solutions, in an intermediate step in the processing of uranium ores. It is a step in the processing of uranium after it has been mined but before fuel fabrication or uranium enrichment. Yellowcake concentrates are prepared by various extraction and refining methods, depending on the types of ores. Typically, yellowcakes are obtained through the milling and chemical processing of uranium ore, forming a coarse powder that has a pungent odor, is insoluble in water, and contains about 80% uranium oxide, which melts at approximately 2880 °C.

<span class="mw-page-title-main">Autunite</span>

Autunite (hydrated calcium uranyl phosphate), with formula Ca(UO2)2(PO4)2·10–12H2O, is a yellow-greenish fluorescent phosphate mineral with a hardness of 2–2+1⁄2. Autunite crystallizes in the orthorhombic system and often occurs as tabular square crystals, commonly in small crusts or in fan-like masses. Due to the moderate uranium content of 48.27% it is radioactive and also used as uranium ore. Autunite fluoresces bright green to lime green under UV light. The mineral is also called calco-uranite, but this name is rarely used and effectively outdated.

<span class="mw-page-title-main">Torbernite</span> Copper uranyl phosphate mineral

Torbernite, also known as chalcolite, is a relatively common mineral with the chemical formula Cu[(UO2)(PO4)]2(H2O)12. It is a radioactive, hydrated green copper uranyl phosphate, found in granites and other uranium-bearing deposits as a secondary mineral. The chemical formula of torbernite is similar to that of autunite in which a Cu2+ cation replaces a Ca2+ cation. Torbernite tends to dehydrate to metatorbernite with the sum formula Cu[(UO2)(PO4)]2(H2O)8.

<span class="mw-page-title-main">Zippeite</span>

Zippeite is a hydrous potassium uranium sulfate mineral with formula: K4(UO2)6(SO4)3(OH)10·4(H2O). It forms yellow to reddish brown monoclinic-prismatic crystals with perfect cleavage. The typical form is as encrustations and pulverulent earthy masses. It forms as efflorescent encrustations in underground uranium mines. It has a Mohs hardness of 2 and a specific gravity of 3.66. It is strongly fluorescent yellow under ultraviolet light and is moderately radioactive.

<span class="mw-page-title-main">Uranium oxide</span> Oxide of the element uranium

Uranium oxide is an oxide of the element uranium.

<span class="mw-page-title-main">Uranium trioxide</span> Chemical compound

Uranium trioxide (UO3), also called uranyl oxide, uranium(VI) oxide, and uranic oxide, is the hexavalent oxide of uranium. The solid may be obtained by heating uranyl nitrate to 400 °C. Its most commonly encountered polymorph, γ-UO3, is a yellow-orange powder.

<span class="mw-page-title-main">Uranyl peroxide</span> Chemical compound

Uranyl peroxide or uranium peroxide hydrate (UO4·nH2O) is a pale-yellow, soluble peroxide of uranium. It is found to be present at one stage of the enriched uranium fuel cycle and in yellowcake prepared via the in situ leaching and resin ion exchange system. This compound, also expressed as UO3·(H2O2)·(H2O), is very similar to uranium trioxide hydrate UO3·nH2O. The dissolution behaviour of both compounds are very sensitive to the hydration state (n can vary between 0 and 4). One main characteristic of uranium peroxide is that it consists of small needles with an average AMAD of about 1.1 μm.

<span class="mw-page-title-main">Metatorbernite</span>

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<span class="mw-page-title-main">Schoepite</span>

Schoepite, empirical formula (UO2)8O2(OH)12·12(H2O) is a rare alteration product of uraninite in hydrothermal uranium deposits. It may also form directly from ianthinite. The mineral presents as a transparent to translucent yellow, lemon yellow, brownish yellow, or amber orthorhombic tabular crystals. Although over 20 other crystal forms have been noted; rarely in microcrystalline aggregates. When exposed to air schoepite converts over a short time to the metaschoepite form (UO3·nH2O, n < 2) within a few months of being exposed to ambient air.

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<span class="mw-page-title-main">Bergenite</span>

Bergenite is a rare uranyl phosphate of the more specific phosphuranylite group. The phosphuranylite-type sheet in bergenite is a new isomer of the group, with the uranyl phosphate tetrahedra varying in an up-up-down, same-same-opposite (uuduudSSOSSO) orientation. All bergenite samples have been found in old mine dump sites. Uranyl minerals are a large constituent of uranium deposits.

<span class="mw-page-title-main">Boltwoodite</span> Hydrated potassium uranyl silicate mineral

Boltwoodite is a hydrated uranyl silicate mineral with formula (K0.56Na0.42)[(UO2)(SiO3OH)]·1.5(H2O), distinct in crystal structure from sodium boltwoodite, which has an orthorhombic structure rather than monoclinic. It is formed from the oxidation and alteration of primary uranium ores. It takes the form of a crust on some sandstones that bear uranium. These crusts tend to be yellowish with a silky or vitreous luster.

<span class="mw-page-title-main">Curite</span>

Curite is a rare mineral with the chemical composition Pb3[(UO2)4|O4|(OH)3]2·2 H2O. It is therefore a hydrated lead uranyl oxide, which forms red needles or orange, massive aggregates.

Bijvoetite-(Y) is a very rare rare-earth and uranium mineral with the formula (Y,REE)8(UO2)16(CO3)16O8(OH)8·39H2O. When compared to the original description, the formula of bijvoetite-(Y) was changed in the course of crystal structure redefinition. Bijvoetite-(Y) is an example of natural salts containing both uranium and yttrium, the other examples being kamotoite-(Y) and sejkoraite-(Y). Bijvoetite-(Y) comes from Shinkolobwe deposit in Republic of Congo, which is famous for rare uranium minerals. The other interesting rare-earth-bearing uranium mineral, associated with bijvoetite-(Y), is lepersonnite-(Gd).

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Plášilite is a very rare uranium mineral with the formula Na2(UO2)(SO4)2•3H2O. Chemically related minerals include natrozippeite, belakovskiite, meisserite, fermiite and oppenheimerite. Most of these uranyl sulfate minerals were originally found in the Blue Lizard mine, San Juan County, Utah, US. The mineral is named after Czech crystallographer Jakub Plášil.

Meyrowitzite, Ca(UO2)(CO3)2·5H2O, is a carbonate mineral verified in May of 2018 by the Commission of New Minerals, Nomenclature and Classification of the International Mineralogical Association. It is an extremely rare mineral, discovered in the Markey mine Utah, U.S.A. The mineral is a transparent yellow and has blades up to approximately 0.2 mm in length. It is soluble in water or aqueous solutions. Meyrowitzite is named in honor of Robert Meyrowitz (1916–2013), an American analytical chemist. After serving in WW II, he joined the United States Geological Survey (USGS). He was known for developing innovative new methods for analyzing small and difficult to study mineralogical samples along with his formulation of the high-index immersion liquids.

<span class="mw-page-title-main">Kasolite</span> Lead uranyl silicate monohydrate mineral

Kasolite is an uncommon lead uranyl silicate monohydrate mineral. It is an IMA approved mineral, that had been a valid species before the foundation of the association, that had been first described and published in 1921 by Schoep. It is a grandfathered mineral, meaning the name kasolite is still believed to refer to a valid species to this day. The mineral's name originates from its type locality, namely the Shinkolobwe Mine, also known as Kasolo Mine. Kasolite is possibly the lead analogue of the unnamed phase UM1956-02-SiO:CaHU, and it is the only accepted lead-uranium silicate.

<span class="mw-page-title-main">Gauthierite</span> Hydrous oxyuranyl mineral

Gauthierite is a very rare mineral with the idealised chemical sum formula KPb[(UO2)7O5(OH)7]·8H2O. It is a radioactive, hydrated orange-coloured lead potassium uranyl oxide hydroxide. It was found by analysing old mineral specimens, and is only known from one locality, the Shinkolobwe Mine in the Democratic Republic of the Congo. The mineral was named in honour of Gilbert Gauthier, a Belgian collector of uranium minerals, who provided a sample to one of the co-authors of the study that first identified it in 2017.

References

  1. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
  2. ↑ Mindat Paulscherrerite page
  3. ↑ Mineralienatlas Paulscherrerite page
  4. ↑ Burns, P.C. (1999) The crystal chemistry of uranium. In P.C. Burns and R. Finch. Eds., Uranium: Mineralogy, geochemistry, and the environment, vol.38, 23–90. Reviews in Mineralogy, Mineralogical Society of America, Chantilly, Virginia.
  5. ↑ Finch, R.J., Hawthorne, F.C., Miller, M.L., and Ewing, R.C. (1997) Distinguishing among schoepite, (UO2)8O2(OH)12•12H2O and related minerals by X-ray powder diffraction. Powder Diffraction, 12, 230–238.
  6. 1 2 3 4 5 Brugger, J., Meisser, N., Etschmann, B., Ansermet, S., Pring, A. (2011a) Paulscherrite from the Number 2 Workings, Mt. Painter Inlier, Northern Flinders Ranges, South Australia: “Dehydrated schoepite” is a mineral after all. American Mineralogist, 96, 229–240.
  7. ↑ Finch, R.J., Cooper, M.A., and Hawthorne, F.C. (1996) The crystal structure of schoepite, [(UO2)8O2(OH)12](H2O)12. Canadian Mineralogist, 34, 1071–1088.
  8. ↑ Weller, M.T., Light, M.E., and Gelbrich, T. (2000) Structure of uranium(VI) Oxidedihydrate, UO32H2O; synthetic meta-schoepite (UO2)4O(OH)6 · 5H2O. Acta Crystallographica, B56, 577–583.
  9. ↑ Taylor, J.C. (1971) The structure and form of uranyl hydroxide. Acta Crystallographica, B27, 1088–1091.
  10. ↑ Brugger, J., Foden, J., Wulser, P. (2011b) Genesis and preservation of a uranium-rich paleozoic epithermal system with a surface expression (North Flinders Ranges, South Australia): radiogenic heat driving regional hydrothermal circulation over geological timescales. Astrobiology, 11.6, 499.
  11. ↑ Brugger, J., Krivovichev, S.V., Berlepsch, P., Meisser, N., Ansermet, S., and Armbruster, T. (2004) Spriggite, Pb3(UO2)6O8(OH)2(H2O)3, a new mineral with β-U3O8-type sheets: Description and crystal Structure. American Mineralogist, 89, 339–347.
  12. ↑ Korzeb,S.L., Foord, E.E., and Lichte, F.E. (1997) The chemical evolution and paragenesis of uranium minerals from the Ruggles and Palermo granitic pegmatites, New Hampshire. Canadian Mineralogist, 35, 135–144.
  13. ↑ Finch, R.J. and Ewing, R.C. (1992) The corrosion of uraninite under oxidizing conditions. Journal of Nuclear Materials, 190, 133–156.
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