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]
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.[2] This is in slight opposition to the original reported analysis, that had dysprosium, gadolinium and terbium as main substituting REE.[4]
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 [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]