| Bijvoetite-(Y) | |
| Category: | Carbonate mineral |
| Formula: | (Y,REE)8(UO2)16(CO3)16O8(OH)8•39H2O |
| Imasymbol: | Bij-Y[1] |
| Strunz: | 5.EB.20 (10 ed) 5/F.06-30 (8 ed) |
| Dana: | 16b.2.4.1 |
| System: | Monoclinic |
| Class: | Spheroidal (2) (same H-M symbol) |
| Symmetry: | B21 |
| Unit Cell: | a = 21.23, b = 12.96, c = 44.91 [Å], β = 90.00° (approximated); Z = 4 |
| Color: | Yellow |
| Habit: | Plates |
| Cleavage: | , good |
| Mohs: | 2 |
| Luster: | Vitreous |
| Streak: | Light yellow |
| Diaphaneity: | Transparent to translucent |
| Density: | 3.97 (measured) |
| Opticalprop: | Biaxal (+) |
| Refractive: | nα = 1.60, nβ = 1.65, nγ = 1.72 (approximated) |
| Pleochroism: | Colorless (X), pale yellow (Y), deep yellow (Z) |
| 2V: | 84° (measured) |
| Other: | Radioactive |
| References: | [2] |
Bijvoetite-(Y) is a very rare rare-earth and uranium mineral[3] with the formula (Y,REE)8(UO2)16(CO3)16O8(OH)8·39H2O.[4] When compared to the original description, the formula of bijvoetite-(Y) was changed in the course of crystal structure redefinition.[5] 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).
The mineral is named after the Dutch chemist and crystallographer Johannes Martin Bijvoet.
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. This is in slight opposition to the original reported analysis, that had dysprosium, gadolinium and terbium as main substituting REE.
Bijvoetite-(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.
Although originally thought to be orthorhombic, bijvoetite-(Y) was later shown to be monoclinic. The structural formula of the mineral is [''M''<sup>3+</sup><sub>8</sub><sup>3+</sup>(H<sub>2</sub>O)<sub>25</sub>(UO<sub>2</sub>)<sub>16</sub>O<sub>8</sub>(OH)<sub>8</sub>(CO<sub>3</sub>)<sub>16</sub>](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: