Bergenite is a rare
uranyl
The uranyl ion is an oxycation of uranium in the oxidation state +6, with the chemical formula . 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 ...
phosphate of the more specific phosphuranylite group. The phosphuranylite-type sheet in bergenite is a new isomer of the group, with the
uranyl
The uranyl ion is an oxycation of uranium in the oxidation state +6, with the chemical formula . 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 ...
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
The uranyl ion is an oxycation of uranium in the oxidation state +6, with the chemical formula . 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 ...
minerals are a large constituent of
uranium
Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
deposits.
[Burns, P. and Locock, A. (2003),]
The crystal structure of bergenite, a new geometrical isomer of the phosphuranylite group
, ''Canadian Mineralogist'', 41: 91–101.
The phosphuranylites are one of the two major groups of the uranyl series, and are the most extensive of the
uranium
Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
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.
[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. ]
Structure and composition
The chemical composition given by Locock and Burns was determined by qualitative
electron microprobe
An electron microprobe (EMP), also known as an electron probe microanalyzer (EPMA) or electron micro probe analyzer (EMPA), is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials. It ...
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 Ca
2Ba
4 2)3O2(PO4)2">UO2)3O2(PO4)2sub>3(H
2O)
16.
[ 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 A microprobe is an instrument that applies a stable and well-focused beam of charged particles (electrons or ions) to a sample.
Types
When the primary beam consists of accelerated electrons, the probe is termed an electron microprobe, when the pri ...
analysis gave oxide percentages of P2O5 10.96%. UO3 62.54%, BaO13.96%, CaO 2.44%, and HrO 10.06%.
Uranyl
The uranyl ion is an oxycation of uranium in the oxidation state +6, with the chemical formula . 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 ...
minerals in general are very complicated, with two-thirds of the 173 species’ structures unknown. Bergenite, like other phosphuranylite minerals, consists of uranyl
The uranyl ion is an oxycation of uranium in the oxidation state +6, with the chemical formula . 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 ...
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phosph ...
sheets. Bergenite’s uranyl
The uranyl ion is an oxycation of uranium in the oxidation state +6, with the chemical formula . 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 ...
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phosph ...
sheet is a new geometrical isomer of the group which differs in the orientation of the phosphate tetrahedra
In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the o ...
, and contains H2O along with calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
and barium cations in the interlayer. The structure was determined by direct methods. As proposed by Frost et al., Uranyl
The uranyl ion is an oxycation of uranium in the oxidation state +6, with the chemical formula . 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 ...
pentagonal dipyramids share edges with each other, and are then connected to uranyl hexagonal
In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°.
Regular hexagon
A '' regular hexagon'' has ...
dipyramids on both sides. The hexagonal dipyramids then link with phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phosph ...
tetrahedra
In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the o ...
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).[
Two formula units of the ]unit cell
In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...
contain three UO2O5 pentagonal dipyramids, two UO2O5 hexagonal dipyramids, and three PO4 tetrahedra. The Ba(1) site is in 11-fold coordination with oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
atoms from UO2 polyhedra, and Ba(2) site is in tenfold coordination with UO2 ions and H2O.[ Also included in the structure of bergenite are hydrogen bonded water molecules, with the network displaying very weak to strong ]H-bond
In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a l ...
s. 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.[ The positions of the hydrogens in the ]unit cell
In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...
remain undiscovered.
Physical properties
Bergenite forms as a dark yellow crust with well-developed, small thin needle-like crystals.[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. An original description of bergenite is the orthorhombic symmetry and a density greater than 4.1 g/cm3.[
]
Geologic occurrence and location
Phosphuranylites usually precipitate
In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
from solution containing uranium
Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
, phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
, potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosph ...
, and calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
. 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
Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
, muscovite
Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula K Al2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavag ...
, and plagioclase
Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more pro ...
, especially along cleavage planes.[
Bergenite was first discovered at a now deserted mine dump of the ]SDAG Wismut
SAG/SDAG Wismut was a uranium mining company in East Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populo ...
shaft 254 in Mechelgrun, Vogtland Mining District, Saxony
Saxony (german: Sachsen ; Upper Saxon: ''Saggsn''; hsb, Sakska), officially the Free State of Saxony (german: Freistaat Sachsen, links=no ; Upper Saxon: ''Freischdaad Saggsn''; hsb, Swobodny stat Sakska, links=no), is a landlocked state of ...
, Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
near the city of Bergen, Lower Saxony
Bergen ( Eastphalian: ''Bargen'') is a town in the north of Celle district on the Lüneburg Heath, in Lower Saxony, Germany. Administratively it acts as a municipal borough divided into 12 subordinate parishes based on the town and its surrounding ...
. Other samples have also been found in uranium deposits in the Black Forest
The Black Forest (german: Schwarzwald ) is a large forested mountain range in the state of Baden-Württemberg in southwest Germany, bounded by the Rhine Valley to the west and south and close to the borders with France and Switzerland. It is t ...
, Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
, and in graphitic uranium ore
Uranium ore deposits are economically recoverable concentrations of uranium within the Earth's crust. Uranium is one of the more common elements in the Earth's crust, being 40 times more common than silver and 500 times more common than gold. It ...
in South Korea
South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korean Peninsula and sharing a land border with North Korea. Its western border is formed by the Yellow Sea, while its eas ...
.
Special characteristics
Uranyl phosphates are looked at for environmental concerns, for they are related to hydration-oxidation of used nuclear fuel.[ As Burns suggests, uranyl minerals affect the concentration of uranium in ]groundwater
Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidated ...
and surrounding systems.[Burns, P. (2000)]
"A new uranyl phosphate chain in the structure of parsonsite"
''American Mineralogist
''American Mineralogist: An International Journal of Earth and Planetary Materials'' is a peer-reviewed scientific journal covering the general fields of mineralogy, crystallography, geochemistry, and petrology. It is an official journal of the Min ...
'' 85: 801–805.
See also
* Beraunite
References
{{reflist
External links
Bergenite
at webmineral.com
at uraniumminerals.com
Bergenite
in the Handbook of Mineralogy
Phosphate minerals
Calcium minerals
Barium minerals
Uranium(VI) minerals
Monoclinic minerals
Minerals in space group 14