Bergenite

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Bergenite
Bergenite-144917.jpg
General
Category Uranyl phosphate mineral
Formula
(repeating unit)		Ca2Ba4[(UO2)3O2(PO4)2]3·16(H2O) [1]
or (Ba,Ca)2(UO2)3(PO4)2(OH)4·5.5(H2O) [2]
IMA symbol Bgn [3]
Strunz classification 8.EC.40
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P21/c
Identification
ColorYellow to greenish yellow
Crystal habit Acicular, tabular
Mohs scale hardness2–3
Streak yellow white
Diaphaneity semitransparent
Density 4.1
Optical propertiesBiaxial (-)
Refractive index nα = 1.660 nβ = 1.700 - 1.710 nγ = 1.722
Birefringence δ = 0.062
Other characteristics Radioactive.svg Radioactive, Occurrence: secondary uranium phosphate mineral
References [2] [4]

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. [1]

Contents

The phosphuranylites are one of the two major groups of the uranyl series, and are the most extensive of the uranium minerals. Uranyl phosphates include 45 different minerals, at least 16 of which belong to the phosphuranylite type topology, including dumontite, vanmeersscheite, upalite, and the most characteristic, phosphuranylite. As explained by Frost et al., the uranyl phosphates display diverse chemical and structural features, which often exhibit the geochemical conditions present during formation. [5]

Structure and composition

The chemical composition given by Locock and Burns was determined by qualitative electron microprobe examination on a JEOL JXA-8600 Superprobe at a voltage of 15 kV and current of 0.9 nA. The ideal composition of Bergenite is Ca2Ba4[(UO2)3O2(PO4)2]3(H2O)16. [1] Calcium and barium substitute for each other, with the precise filling of the Ba(1) site 96.8% Ba and 3.2% Ca, and the Ba (2) site containing 87.9% Ba and 12.2% Ca, with Frost (2007) assuming no vacancies and only Ca and Ba substitution. These results give the idealized formula of Ba4/3Ca2/3. A microprobe analysis gave oxide percentages of P2O5 10.96%. UO3 62.54%, BaO13.96%, CaO 2.44%, and HrO 10.06%. [6]

Uranyl minerals in general are very complicated, with two-thirds of the 173 species’ structures unknown. Bergenite, like other phosphuranylite minerals, consists of uranyl phosphate sheets. Bergenite’s uranyl phosphate sheet is a new geometrical isomer of the group which differs in the orientation of the phosphate tetrahedra, and contains H2O along with calcium and barium cations in the interlayer. The structure was determined by direct methods. As proposed by Frost et al., Uranyl pentagonal dipyramids share edges with each other, and are then connected to uranyl hexagonal dipyramids on both sides. The hexagonal dipyramids then link with phosphate tetrahedra to form sheets that connect to adjacent pentagonal chains. The phosphate tetrahedra holding the uranyl chains together display an up-up-down-up-up-down, same-same-opposite orientation (uuduudSSO). [5]

Two formula units of the unit cell contain three UO2O5 pentagonal dipyramids, two UO2O5 hexagonal dipyramids, and three PO4 tetrahedra. The Ba(1) site is in 11-fold coordination with oxygen atoms from UO2 polyhedra, and Ba(2) site is in tenfold coordination with UO2 ions and H2O. [1] Also included in the structure of bergenite are hydrogen bonded water molecules, with the network displaying very weak to strong H-bonds. The inconsistency of the bonds originally caused confusion as to whether it was H2O or OH within the mineral, but further observations of Raman spectra proved it to be water. It is the placement of the water molecules that determines the stability of the structure. [5] The positions of the hydrogens in the unit cell remain undiscovered.

Physical properties

Bergenite forms as a dark yellow crust with well-developed, small thin needle-like crystals. [7] An original description of bergenite is the orthorhombic symmetry and a density greater than 4.1 g/cm3. [1]

Geologic occurrence and location

Phosphuranylites usually precipitate from solution containing uranium, phosphorus, potassium, and calcium. Most phosphuranylite, and all bergenite specimens, are generated from the waste of various mines. This is a low-temperature and often low-pressure process. Bergenite occurs in fractures of quartz, muscovite, and plagioclase, especially along cleavage planes. [7]

Bergenite was first discovered at a now deserted mine dump of the SDAG Wismut shaft 254 in Mechelgrun, Vogtland Mining District, Saxony, Germany near the city of Bergen, Lower Saxony. Other samples have also been found in uranium deposits in the Black Forest, Germany, and in graphitic uranium ore in South Korea.[ citation needed ]

Special characteristics

Uranyl phosphates are looked at for environmental concerns, for they are related to hydration-oxidation of used nuclear fuel. [5] As Burns suggests, uranyl minerals affect the concentration of uranium in groundwater and surrounding systems. [8]

See also

Related Research Articles

<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">Phosphate mineral</span> Nickel–Strunz 9 ed mineral class number 8 (isolated tetrahedral units, mainly)

Phosphate minerals contain the tetrahedrally coordinated phosphate (PO43−) anion, sometimes with arsenate (AsO43−) and vanadate (VO43−) substitutions, along with chloride (Cl−), fluoride (F−), and hydroxide (OH−) anions, that also fit into the crystal structure.

The uranyl ion is an oxycation of uranium in the oxidation state +6, with the chemical formula UO2+
2. It has a linear structure with short U–O bonds, indicative of the presence of multiple bonds between uranium and oxygen. Four or more ligands may be bound to the uranyl ion in an equatorial plane around the uranium atom. The uranyl ion forms many complexes, particularly with ligands that have oxygen donor atoms. Complexes of the uranyl ion are important in the extraction of uranium from its ores and in nuclear fuel reprocessing.

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

Uranopilite is a minor ore of uranium with the chemistry (UO2)6SO4(OH)6O2·14H2O or, hydrated uranyl sulfate hydroxide.

<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">Althupite</span> Aluminium thorium uranyl phosphate mineral

Althupite (IMA symbol: Ahp) is a rare aluminium thorium uranyl phosphate mineral with complex formula written as AlTh(UO2)7(PO4)4O2(OH)5·15H2O, from a granitic pegmatite. It is named after its composition (ALuminium, THorium, Uranium, and Phosphorus).

<span class="mw-page-title-main">Coconinoite</span> Uranium ore

Coconinoite is a uranium ore that was discovered in Coconino County, Arizona. It is a phosphate mineral; or uranyl phosphate mineral along with other subclass uranium U6+ minerals like blatonite, boltwoodite, metazeunerite and rutherfordine.

<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">Phosphuranylite</span>

Phosphuranylite is a uranyl phosphate mineral with formula KCa(H3O)3(UO2)7(PO4)4O4·8(H2O).

<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.

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.

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).

Falsterite is a rare phosphate mineral with the formula Ca2MgMn2+2(Fe2+0.5Fe3+0.5)4Zn4(PO4)8(OH)4(H2O)14. It is a pegmatitic mineral, related to the currently approved mineral ferraioloite.

Meisserite is a very rare uranium mineral with the formula Na5(UO2)(SO4)3(SO3OH)(H2O). It is interesting in being a natural uranyl salt with hydrosulfate (hydroxysulfate) anion, a feature shared with belakovskiite. Other chemically related minerals include fermiite, oppenheimerite, natrozippeite and plášilite. Most of these uranyl sulfate minerals was originally found in the Blue Lizard mine, San Juan County, Utah, USA. The mineral is named after Swiss mineralogist Nicolas Meisser.

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.

Cattiite is a phosphate mineral. The mineral was first found in a veins of dolomite carbonatites veins at the bottom of the Zhelezny (Iron) Mine in the Kovdor massif, Kola Peninsula, Russia. Cattiite was tentatively identified as Mg3(PO4)2·22H2O, which as a high hydrate magnesium orthophosphate. Later structural studies, revealed the existence of two polytypes named Mg3(PO4)2·22H2O-1A1 and Mg3(PO4)2·22H2O-1A2.

<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.

Greenlizardite is a rare sulfate mineral discovered underground in the Green Lizard Mine, which the mineral was named for, in Utah. The mineral was found in mineralized ore channels within the Shinarump member of the Chinle formation. It occurs as a secondary alteration phase. It is associated with ammoniozippeite, boussingaultite, and dickite. Greenlizardite was approved as a mineral by the International Mineralogical Association in 2017.

Uramphite is a rarely-found phosphate mineral in the "phosphate, arsenate and vanadate" mineral class with chemical composition (NH4)2[UO2PO4]2·6H2O from which it is seen to be a hydrated ammonium uranyl phosphate.

References

  1. 1 2 3 4 5 Burns, P. and Locock, A. (2003), "The crystal structure of bergenite, a new geometrical isomer of the phosphuranylite group", Canadian Mineralogist, 41: 91–101.
  2. 1 2 http://rruff.geo.arizona.edu/doclib/hom/bergenite.pdf Handbook of Mineralogy
  3. ↑ 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.
  4. ↑ http://www.mindat.org/min-631.html Mindat.org
  5. 1 2 3 4 Frost, R., Cejka, J., Ayoko, G., Weier, M. (2007), "A Raman spectroscopic study of the uranyl phosphate mineral bergenite", Spectrochimica Acta Part A-Molecular and Biomolecular Spectroscopy 66: 979–984. doi : 10.1016/j.saa.2006.04.036
  6. ↑ Cabri, J., Fleischer, M., and Pabst, A. (1981), "New Mineral Names", American Mineralogist 66: 1099–1103.
  7. 1 2 Korzeb, S., Foord, E., and Lichte F. (1997), "The chemical evolution and paragenesis of uranium minerals from the Ruggles and Palermo granitic pegmatites, New Hampshire", Canadian Mineralogist 35: 135–144.
  8. ↑ Burns, P. (2000), "A new uranyl phosphate chain in the structure of parsonsite", American Mineralogist 85: 801–805.
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