Bijvoetite-(Y) is a very rare rare-earth and

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 ...

mineralDeliens, M., and Piret, P., 1982. Bijvoetite et lepersonnite, carbonates hydrates d'uranyle et des terres rares de Shinkolobwe, Zaïre. Canadian Mineralogist 20, 231-238 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.Li, Y., Burns, P. C., and Gault, R. A., 2000. A new rare-earth-element uranyl carbonate sheet in the structure of bijvoetite-(Y). The Canadian Mineralogist 38, 153-162. 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) Lepersonnite-(Gd) is a very rare rare-earth and uranium mineral with the chemical formula . It occurs associated with bijvoetite-(Y) in the Shinkolobwe deposit in the Democratic Republic of the Congo, famous for rare uranium minerals. Lepersonnite ...

. The mineral is named after the Dutch

chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe th ...

and crystallographer Johannes Martin Bijvoet.

Notes on chemistry

Other rare-earth elements substituting for yttrium ("REE" in the given formula) are mainly

neodymium Neodymium is a chemical element with the symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishes i ...

, samarium, gadolinium, and

dysprosium Dysprosium is the chemical element with the symbol Dy and atomic number 66. It is a rare-earth element in the lanthanide series with a metallic silver luster. Dysprosium is never found in nature as a free element, though, like other lanthanides, it ...

, with minor

cerium Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 o ...

europium Europium is a chemical element with the symbol Eu and atomic number 63. Europium is the most reactive lanthanide by far, having to be stored under an inert fluid to protect it from atmospheric oxygen or moisture. Europium is also the softest lanth ...

, terbium and

erbium Erbium is a chemical element with the symbol Er and atomic number 68. A silvery-white solid metal when artificially isolated, natural erbium is always found in chemical combination with other elements. It is a lanthanide, a rare-earth element ...

. This is in slight opposition to the original reported analysis, that had

, gadolinium and terbium as main substituting REE.

Occurrence and association

Bijvoetite-(Y) was found in the Shinkolobwe dolomite-hosted uranium deposit,

Republic of Congo The Republic of the Congo (french: République du Congo, ln, Republíki ya Kongó), also known as Congo-Brazzaville, the Congo Republic or simply either Congo or the Congo, is a country located in the western coast of Central Africa to the w ...

, where it occurs in an oxidation zone, together with numerous other uranium minerals:

, becquerelite, curite, kasolite, oursinite, rutherfordine, schoepite, sklodowskite, soddyite, studtite, torbernite, and uranophane.

Crystal structure

Although originally though to be orthorhombic, bijvoetite-(Y) was later shown to be monoclinic. The structural formula of the mineral is 'M''³⁺₈³⁺(H₂O)₂₅(UO₂)₁₆O₈(OH)₈(CO₃)₁₆H₂O)₁₄, where ''M'' = (Y,REE). The structure has 16 uranium sites, with uranium belonging to near-linear

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 ...

groups. The important features of the structure are: * presence of uranyl pentagonal bipyramids (UPB), formed by coordination of (eight)

groups by three oxide and two

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...

anions * presence of uranyl hexagonal bipyramids (UHB), formed by coordination of another eight

groups by six oxide anions * presence of uranyl carbonate chain parallel to 00 of a novel type, built of edge-sharing dimers of UPB and UHB, and

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...

groups * presence of irregular ''M''³⁺Φ_n polyhedra (Φ - unspecified ligand) linking the uranyl carbonate chain, thus forming a compound novel-type sheet parallel to (010) * location of 14 water molecules in the interlayer space (held by hydrogen bonding) * bonding of the remaining 25 water molecules to trivalent cations

References

{{reflist Uranium(VI) minerals Yttrium minerals Lanthanide minerals Carbonate minerals Monoclinic minerals Minerals in space group 4