The importance of accurate crystal structure determination of uranium minerals. I. Phosphuranylite KCa(H3O)3(UO2)7(PO4)4O4.8H2O

Demartin, Francesco; Diella, Valeria; Donzelli, Stefano; Gramaccioli, C. M.; Pilati, Tullio

doi:10.1107/s010876819100099x

Cited by 54 publications

(45 citation statements)

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“…On the basis of the changes in K w with temperature and pressure, it is proposed that the formation of pentagonite or cavansite depends on whether or not the hydrothermal solution is in supercritical condition (above 300 °C). Such a difference in the formation of cavansite and pentagonite cannot be verified by comparing the crystallization temperatures of H 3 O + -bearing minerals such as jarosite -alunite groups (Ripmeester et al, 1986;Lager et al, 2001), hydrated uranates (Demartin et al, 1991;Chukanov et al, 1999;Chukanov et al, 2004), and clay min- Table 9. Assignment of hydrogens to the refined oxygens using the difference in bond -valence sum of cavansite Polymorphic relation between cavansite and pentagonite erals (Jiang et al, 1994).…”

Section: Polymorphic Relation Between Cavansite and Pentagonitementioning

confidence: 99%

Polymorphic relation between cavansite and pentagonite: Genetic implications of oxonium ion in cavansite

Ishida

Kimata

Nishida

et al. 2009

Journal of Mineralogical and Petrological Sciences

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The chemical compositions of cavansite and pentagonite, in which H 2 O contents and vanadium (in an unknown oxidation state) are present, were determined by thermogravimetry -differential thermal analysis (TG -DTA), electron spin resonance (ESR), and electron microprobe analysis (EMPA). Furthermore, the mechanism of dehydration of the minerals and presence of the hydrous species such as H 2 O, H 3 O + , and OH − in the aforementioned minerals have been investigated by TG -DTA, high -temperature X -ray diffraction (HT -XRPD) analysis, Fourier -transform infrared (FTIR) spectroscopy, and single -crystal XRD analysis. The results of TG -DTA and HT -XRD revealed that no reversible transitions occur between cavansite and pentagonite when they are heated in air and that no intermediate amorphous phase exists in these two minerals. Gradual dehydration of cavansite in the temperature range of 225 -550 °C was attributed to the removal of both oxonium (H 3 O + ) and hydroxyl ions (OH − ); the IR absorption bands of cavansite observed at 3186 and 3653 cm −1 were assigned to H 3 O + and OH − stretching vibrations, respectively. Moreover, the exact distribution of hydrogens in the crystal structure of the cavansite refined in this study was determined by applying the valence -matching principle; the results showed the existence of H 3 O + and OH − . Thus, the structural formula of cavansite should be revised to Ca(VO)(Si 4 O 10 )·(H 2 O) 4−2x (H 3 O) x (OH) x , in contrast to that of pentagonite, Ca(VO)(Si 4 O 10 )·4H 2 O. The changes in the ion product constant of water with temperature and pressure suggest that pentagonite is formed when the hydrothermal fluid is in supercritical condition (>300 °C), while cavansite is formed when the hydrothermal fluid is not in supercritical condition. Thus, cavansite is identified as a low -temperature form and pentagonite as a high -temperature one.

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Section: Polymorphic Relation Between Cavansite and Pentagonitementioning

confidence: 99%

Polymorphic relation between cavansite and pentagonite: Genetic implications of oxonium ion in cavansite

Ishida

Kimata

Nishida

et al. 2009

Journal of Mineralogical and Petrological Sciences

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“…23) Demartin et al (1991) has not been proved by study of infrared absorption spectra (Čejka 1999). Demartin et al (1991) and Piret et al (1990) derived the chemical formulae of dewindtite and phosphuranylite from analyses of crystal structures, which were not supported by reliable data on chemical composition.…”

Section: Phosphuranylite Group Mineralsmentioning

confidence: 99%

“…The dominating anion in the tetrahedral site of saléeite I (Fig. 29) (Demartin et al 1991) 4.2.7. Saléeite Mg(UO 2 ) 2 (PO 4 ) 2 · 10H 2 O Crystallized saléeite is a common mineral among the recently studied samples from Medvědín.…”

Section: Phosphuranylite Group Mineralsmentioning

confidence: 99%

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Supergene mineralization of the Medvědín uranium deposit, Krkonoše Mountains, Czech Republic

Plášil¹,

Sejkora²,

Čejka³

et al. 2012

Jour. Geosci.

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Supergene mineralization of the hydrothermal vein uranium deposit Medvědín (Krkonoše Mts., northern Bohemia) is rather varied both in number of the mineral phases and their chemical variation. The supergene minerals agardite-(Y), autunite/metaautunite, dewindtite, churchite-(Y), kasolite, new unnamed phase Pb(Ce,REE) 3 (PO 4 ) 3 (OH) 2 . nH 2 O, parsonsite, phosphuranylite, plumbogummite, pseudomalachite, pyromorphite, saléeite, torbernite/metatorbernite and uranophane were studied using powder XRD, EPMA, IR-spectroscopic and thermal analysis, contributing significantly to the clarification of their crystal chemistry. The alteration mineral assemblage consisting mostly of uranyl phosphates and silicates exhibits relatively high contents of REE and Pb. Minerals with a composition corresponding to pure mineral end-members have not been observed; instead most of the studied phases represent members of isomorphic series. Studied mineral assemblage is a stable association in surface conditions resulting apparently from a long-term alteration of the primary uranium mineralization.

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“…In light of the lack of agreement concerning the presence of K in phosphuranylite (Demartin et al 1991, Piret & Piret-Meunier 1991, the chemical composition of bergenite was confirmed by qualitative electron-microprobe examination. Crystals of bergenite were mounted on an adhesive carbon tab and carbon-coated.…”

Section: Electron-microprobe Examinationmentioning

confidence: 99%

The Crystal Structure of Bergenite, a New Geometrical Isomer of the Phosphuranylite Group

Locock¹,

Burns²

2003

The Canadian Mineralogist

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The crystal structure of bergenite, ideally Ca 2 Ba 4 [(UO 2 ) 3 O 2 (PO 4 ) 2 ] 3 (H 2 O) 16 , monoclinic, space group P2 1 /c, a 10.092(1), b 17.245(2), c 17.355(2) Å, ␤ 113.678(2)°, V 2766.2(3) Å 3 , Z = 2, D calc 4.82 g/cm 3 , was solved by direct methods and refined by full-matrix least-squares techniques on the basis of F 2 to agreement indices R1 of 5.0% calculated for 4118 unique observed reflections (|F o | ≥ 4 F ), and wR 2 of 11.9% for all data. Intensity data were collected at room temperature using MoK␣ radiation and a CCD-based area detector. The structure of bergenite contains five symmetrically independent uranium atoms, each of which is part of a (UO 2 ) 2+ uranyl ion. The uranyl ions of U(1), U(2) and U(3) are coordinated by five additional ligands giving pentagonal bipyramids, and the uranyl ions of U(4) and U(5) are coordinated by six additional ligands yielding hexagonal bipyramids. The uranyl pentagonal bipyramids share edges, forming dimers, which are linked to uranyl hexagonal bipyramids on either side, resulting in chains of bipyramids. Each uranyl hexagonal bipyramid shares two equatorial edges with phosphate tetrahedra, and the resulting uranyl phosphate chains are linked into sheets by the sharing of vertices of phosphate tetrahedra with uranyl pentagonal bipyramids of adjacent chains. The uranyl phosphate sheet in bergenite is a new geometrical isomer of the phosphuranylite group; the phosphate tetrahedra between the uranyl chains vary orientations in an up-up-down up-up-down (uuduud) pattern, and the pairs of tetrahedra attached to uranyl hexagonal bipyramids change orientations in a complementary same-same-opposite (SSO) manner (symbol uuduudSSO). In bergenite, the uranyl phosphate sheets are oriented parallel to (102), and the interlayer contains one calcium atom, two barium atoms and eight symmetrically distinct H 2 O groups.Keywords: bergenite, phosphuranylite, uranyl phosphate, geometrical isomer, crystal structure. SOMMAIRENous avons résolu la structure cristalline de la bergenite, de formule idéale Ca 2 Ba 4 [(UO 2 ) 3 O 2 (PO 4 ) 2 ] 3 (H 2 O) 16 , monoclinique, groupe spatial P2 1 /c, a 10.092(1), b 17.245(2), c 17.355(2) Å, ␤ 113.678(2)°, V 2766.2(3) Å 3 , Z = 2, D calc 4.82 g/cm 3 , par méthodes directes, et nous l'avons affinée par moindres carrés sur matrice entière en utilisant les facteurs F 2 jusqu'à un résidu R1 de 5.0% calculé avec 4118 réflexions uniques observées (|F o | ≥ 4 F ), et wR 2 de 11.9% pour toutes les données. L'intensité des réflexions a été mesurée à température ambiante avec un rayonnement MoK␣ et un détecteur à aire de type CCD. La structure de la bergenite contient cinq atomes d'uranium symétriquement indépendants, chacun faisant partie d'un ion uranyle, (UO 2 ) 2+ . Les ions uranyles U(1), U(2) et U(3) ont des liaisons à cinq ligands additionnels, ce qui donne des bipyramides pentagonales, et les ions uranyles U(4) et U(5) ont des liaisons à six ligands additionnels, ce qui donne des bipyramides hexagonales. Les bipyramides pentagonales...

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The importance of accurate crystal structure determination of uranium minerals. I. Phosphuranylite KCa(H₃O)₃(UO₂)₇(PO₄)₄O₄.8H₂O

Cited by 54 publications

References 1 publication

Polymorphic relation between cavansite and pentagonite: Genetic implications of oxonium ion in cavansite

Polymorphic relation between cavansite and pentagonite: Genetic implications of oxonium ion in cavansite

Supergene mineralization of the Medvědín uranium deposit, Krkonoše Mountains, Czech Republic

The Crystal Structure of Bergenite, a New Geometrical Isomer of the Phosphuranylite Group

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