Bijvoetite-(Y) is a very rare rare-earth and uranium mineral[3][4] with the formula (Y,REE)8(UO2)16(CO3)16O8(OH)8·39H2O.[4][5] When compared to the original description, the formula of bijvoetite-(Y) was changed in the course of crystal structure redefinition.[2] Bijvoetite-(Y) is an example of natural salts containing both uranium and yttrium, the other examples being kamotoite-(Y) and sejkoraite-(Y).[6][7] 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).[3]
| Bijvoetite-(Y) | |
|---|---|
| General | |
| Category | Carbonate mineral |
| Formula (repeating unit) | (Y,REE)8(UO2)16(CO3)16O8(OH)8•39H2O |
| IMA symbol | Bij-Y[1] |
| Strunz classification | 5.EB.20 (10 ed) 5/F.06-30 (8 ed) |
| Dana classification | 16b.2.4.1 |
| Crystal system | Monoclinic |
| Crystal class | Spheroidal (2) (same H-M symbol) |
| Space group | B21 |
| Unit cell | a = 21.23, b = 12.96, c = 44.91 [Å], β = 90.00° (approximated); Z = 4 |
| Identification | |
| Color | Yellow |
| Crystal habit | Plates |
| Cleavage | {001}, good |
| Mohs scale hardness | 2 |
| Luster | Vitreous |
| Streak | Light yellow |
| Diaphaneity | Transparent to translucent |
| Density | 3.97 (measured) |
| Optical properties | Biaxal (+) |
| Refractive index | nα = 1.60, nβ = 1.65, nγ = 1.72 (approximated) |
| Pleochroism | Colorless (X), pale yellow (Y), deep yellow (Z) |
| 2V angle | 84° (measured) |
| Other characteristics |  Radioactive |
| References | [2][3][4][5] |
The mineral is named after the Dutch chemist and crystallographer Johannes Martin Bijvoet.
Notes on chemistry
editOther rare-earth elements substituting for yttrium ("REE" in the given formula) are mainly neodymium, samarium, gadolinium, and dysprosium, with minor cerium, europium, terbium and erbium.[2] This is in slight opposition to the original reported analysis, that had dysprosium, gadolinium and terbium as main substituting REE.[4]
Occurrence and association
editBijvoetite-(Y) was found in the Shinkolobwe dolomite-hosted uranium deposit, Republic of Congo, where it occurs in an oxidation zone, together with numerous other uranium minerals: lepersonnite-(Gd), becquerelite, curite, kasolite, oursinite, rutherfordine, schoepite, sklodowskite, soddyite, studtite, torbernite, and uranophane.
Crystal structure
editAlthough originally thought to be orthorhombic, bijvoetite-(Y) was later shown to be monoclinic. The structural formula of the mineral is [M3+83+(H2O)25(UO2)16O8(OH)8(CO3)16](H2O)14, where M = (Y,REE). The structure has 16 uranium sites, with uranium belonging to near-linear uranyl groups. The important features of the structure are:[2]
- presence of uranyl pentagonal bipyramids (UPB), formed by coordination of (eight) uranyl groups by three oxide and two hydroxyl anions
- presence of uranyl hexagonal bipyramids (UHB), formed by coordination of another eight uranyl groups by six oxide anions
- presence of uranyl carbonate chain parallel to [100], of a novel type, built of edge-sharing dimers of UPB and UHB, and carbonate groups
- presence of irregular M3+Φn 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
edit- ^ 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.
- ^ a b c d 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.
- ^ a b c Deliens, M., and Piret, P., 1982. Bijvoetite et lepersonnite, carbonates hydrates d'uranyle et des terres rares de Shinkolobwe, Zaïre. Canadian Mineralogist 20, 231-238
- ^ a b c d "Bijvoetite-(Y) - Handbook of Mineralogy" (PDF). Handbookofmineralogy.org. Retrieved 2016-03-12.
- ^ a b "Bijvoetite-(Y): Bijvoetite-(Y) mineral information and data". Mindat.org. Retrieved 2016-03-04.
- ^ "Kamotoite-(Y): Kamotoite-(Y) mineral information and data". Mindat.org. Retrieved 2016-03-10.
- ^ "Sejkoraite-(Y): Sejkoraite-(Y) mineral information and data". Mindat.org. Retrieved 2016-03-10.