Bergenite is a rare

uranyl The uranyl ion with the chemical formula has a linear structure with short U–O bonds, indicative of the presence of multiple bonds between uranium and oxygen, with uranium in the oxidation state +6. Four or more ligands may be bound to the u ...

phosphate of the more specific phosphuranylite group. The phosphuranylite-type sheet in bergenite is a new isomer of the group, with the

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 with the chemical formula has a linear structure with short U–O bonds, indicative of the presence of multiple bonds between uranium and oxygen, with uranium in the oxidation state +6. Four or more ligands may be bound to the u ...

minerals are a large constituent of

uranium Uranium is a chemical element; it has chemical symbol, 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. Ura ...

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

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. I ...

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)₂sub>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 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 pr ...

analysis gave

oxide An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...

percentages of P₂O₅ 10.96%. UO₃ 62.54%, BaO13.96%, CaO 2.44%, and HrO 10.06%.

minerals in general are very complicated, with two-thirds of the 173 species’ structures unknown. Bergenite, like other phosphuranylite minerals, consists of

phosphate Phosphates are the naturally occurring form of the element phosphorus. 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 orthop ...

sheets. Bergenite’s

sheet is a new geometrical isomer of the group which differs in the orientation of the phosphate

tetrahedra In geometry, a tetrahedron (: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular Face (geometry), faces, six straight Edge (geometry), edges, and four vertex (geometry), vertices. The tet ...

, and contains H₂O along with

calcium Calcium is a chemical element; it has 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 to it ...

and

barium Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. Th ...

cations in the interlayer. The structure was determined by direct methods. As proposed by Frost et al.,

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 is d ...

dipyramids on both sides. The hexagonal dipyramids then link with

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 In mathematics, a unit vector i ...

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 a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

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 In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...

ed water molecules, with the network displaying very weak to strong

H-bond In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, covalently bonded to a more ...

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

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 "sedimentation of a solid material (a precipitate) from a liquid solution". The solid formed is called the precipitate. In case of an inorganic chemical reaction leading to precipitation, the chemic ...

from solution containing

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

, and

. 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 Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

muscovite Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula KAl2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavage y ...

, and

plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...

, especially along

cleavage planes Cleavage, in mineralogy and materials science, 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 ...

. 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 during the time of the Cold War. It produced a total of 230,400 tonnes of uranium between 1947 and 1990 and made East Germany the fourth largest producer of uranium ore in the world a ...

shaft 254 in Mechelgrun, Vogtland Mining District,

Saxony Saxony, officially the Free State of Saxony, is a landlocked state of Germany, bordering the states of Brandenburg, Saxony-Anhalt, Thuringia, and Bavaria, as well as the countries of Poland and the Czech Republic. Its capital is Dresden, and ...

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

near the city of

Bergen, Lower Saxony Bergen (; Eastphalian dialect, Eastphalian: ''Bargen'') is a town in the north of Celle (district), Celle district on the Lüneburg Heath, in Lower Saxony, Germany. Administratively it acts as a municipal borough divided into 12 subordinate parish ...

. Other samples have also been found in uranium deposits in the

Black Forest The Black Forest ( ) is a large forested mountain range in the States of Germany, 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 th ...

, and in

graphitic Graphite () is a crystalline allotrope (form) of the element carbon. It consists of many stacked layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable form of carbon under standard cond ...

uranium ore Uranium ore deposits are economically recoverable concentrations of uranium within Earth's crust. Uranium is one of the most common Chemical element, elements in Earth's crust, being 40 times more common than silver and 500 times more common than ...

South Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia. It constitutes the southern half of the Korea, Korean Peninsula and borders North Korea along the Korean Demilitarized Zone, with the Yellow Sea to the west and t ...

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 Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...

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 Mi ...

'' 85: 801–805.

References

External links

Bergenite
at webmineral.com

at uraniumminerals.com
Bergenite
{{Webarchive, url=https://web.archive.org/web/20110726142259/http://www.handbookofmineralogy.org/pdfs/bergenite.pdf , date=2011-07-26 in the Handbook of Mineralogy Phosphate minerals Calcium minerals Barium minerals Uranium(VI) minerals Monoclinic minerals Minerals in space group 14