Bijvoetite-(Y)
| Bijvoetite-(Y) | |
|---|---|
| General | |
| Category | Carbonate mineral |
| Formula (repeating unit) | (Y,REE)8(UO2)16(CO3)16O8(OH)8•39H2O |
| 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) H-M symbol: (2) |
| 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 | 84o (measured) |
| Other characteristics | Radioactive |
| References | [1][2][3][4] |
Bijvoetite-(Y) is a very rare rare earth and uranium mineral[2][3] with the formula (Y,REE)8(UO2)16(CO3)16O8(OH)8•39H2O.[3][4] When compared to the original description, the formula of bijvoetite-(Y) was changed in curse of crystal structure redefinition.[1] Bijvoetite-(Y) is an example of natural salts containing both uranium and yttrium, the other examples being kamotoite-(Y) and sejkoraite-(Y).[5][6] 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).[2]
Notes on chemistry
Other 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.[1] This is in slight opposition to the original reported analysis, that had dysprosium, gadolinium and terbium as main substituting REE.[3]
Occurrence and association
Bijvoetite-(Y) was found in Shinkolobwe dolomite-hosted uranium deposit, Rep. 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
Although originally though 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:[1]
- 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
- 1 2 3 4 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.
- 1 2 3 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
- 1 2 3 4 "Bijvoetite-(Y) - Handbook of Mineralogy" (PDF). Handbookofmineralogy.org. Retrieved 2016-03-12.
- 1 2 "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.