Bergenite
Encyclopedia
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.
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.
examination on a JEOL JXA-8600 Superprobe at a voltage of 15kV and current of 0.9 nA. The ideal composition of Bergenite is Ca2Ba4[(UO2)3O2(PO4)2]3(H2O)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
analysis gave oxide
percentages of P2O5 10.96%. UO3 62.54%, BaO13.96%, CaO 2.44%, and HrO 10.06%.
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).
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. Also included in the structure of bergenite are hydrogen bond
ed 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. The positions of the hydrogens in the unit cell remain undiscovered.
, 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
.
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
.
and surrounding systems.
Uranyl
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 are bound to the uranyl ion in an equatorial plane...
phosphate of the more specific phosphuranylite group. The phosphuranylite-type sheet in bergenite is a new isomer of the group, with the uranyl
Uranyl
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 are bound to the uranyl ion in an equatorial plane...
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
Uranyl
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 are bound to the uranyl ion in an equatorial plane...
minerals are a large constituent of uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
deposits.
The phosphuranylites are one of the two major groups of the uranyl series, and are the most extensive of the uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
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.
Structure and composition
The chemical composition given by Locock and Burns was determined by qualitative electron microprobeElectron microprobe
An electron microprobe , also known as an electron probe microanalyzer or electron micro probe analyzer , is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials...
examination on a JEOL JXA-8600 Superprobe at a voltage of 15kV and current of 0.9 nA. The ideal composition of Bergenite is Ca2Ba4[(UO2)3O2(PO4)2]3(H2O)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
Microprobe
A microprobe is an instrument that applies a stable and well-focused beam of charged particles to a sample.-Types:When the primary beam consists of accelerated electrons, the probe is termed an electron microprobe, when the primary beam consists of accelerated ions, the term Ion Microprobe is used...
analysis gave oxide
Oxide
An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....
percentages of P2O5 10.96%. UO3 62.54%, BaO13.96%, CaO 2.44%, and HrO 10.06%.
Uranyl
Uranyl
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 are bound to the uranyl ion in an equatorial plane...
minerals in general are very complicated, with two-thirds of the 173 species’ structures unknown. Bergenite, like other phosphuranylite minerals, consists of uranyl
Uranyl
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 are bound to the uranyl ion in an equatorial plane...
phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
sheets. Bergenite’s uranyl
Uranyl
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 are bound to the uranyl ion in an equatorial plane...
phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
sheet is a new geometrical isomer of the group which differs in the orientation of the phosphate tetrahedra, and contains H2O along with calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
and barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
cations in the interlayer. The structure was determined by direct methods. As proposed by Frost et al., Uranyl
Uranyl
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 are bound to the uranyl ion in an equatorial plane...
pentagonal dipyramids share edges with each other, and are then connected to uranyl hexagonal
Hexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
dipyramids on both sides. The hexagonal dipyramids then link with phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
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).
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
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
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 bond
Hydrogen bond
A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine, that comes from another molecule or chemical group. The hydrogen must be covalently bonded to another electronegative atom to create the bond...
ed 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
Raman spectroscopy
Raman spectroscopy is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system.It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range...
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 remain undiscovered.
Physical properties
Bergenite forms as a dark yellow crust with well-developed, small thin needle-like crystals. 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 from solution containing uraniumUranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
, phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
, potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
, and calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
. 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
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
, muscovite
Muscovite
Muscovite is a phyllosilicate mineral of aluminium and potassium with formula KAl22, or 236. It has a highly-perfect basal cleavage yielding remarkably-thin laminæ which are often highly elastic...
, and plagioclase
Plagioclase
Plagioclase is an important series of tectosilicate minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series...
, especially along cleavage planes
Cleavage (crystal)
Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the...
.
Bergenite was first discovered at a now deserted mine dump of the SDAG Wismut shaft 254 in Mechelgrun, Vogtland Mining District, Saxony
Saxony
The Free State of Saxony is a landlocked state of Germany, contingent with Brandenburg, Saxony Anhalt, Thuringia, Bavaria, the Czech Republic and Poland. It is the tenth-largest German state in area, with of Germany's sixteen states....
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
near the city of Bergen, Lower Saxony
Bergen, Lower Saxony
Bergen 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 villages: Becklingen, Belsen, Bergen, Bleckmar, Diesten, Dohnsen, Eversen,...
. Other samples have also been found in uranium deposits in the Black Forest
Black Forest
The Black Forest is a wooded mountain range in Baden-Württemberg, southwestern Germany. It is bordered by the Rhine valley to the west and south. The highest peak is the Feldberg with an elevation of 1,493 metres ....
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, and in graphitic
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
uranium ore in South Korea
South Korea
The Republic of Korea , , is a sovereign state in East Asia, located on the southern portion of the Korean Peninsula. It is neighbored by the People's Republic of China to the west, Japan to the east, North Korea to the north, and the East China Sea and Republic of China to the south...
.
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 groundwaterGroundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...
and surrounding systems.