Bijvoetite-(Y)


Bijvoetite- is a very rare rare-earth and uranium mineral with the formula 81616O88·39H2O. When compared to the original description, the formula of bijvoetite- was changed in the course of crystal structure redefinition. Bijvoetite- is an example of natural salts containing both uranium and yttrium, the other examples being kamotoite- and sejkoraite-. Bijvoetite- 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-, is lepersonnite-(Gd).
The mineral is named after the Dutch chemist and crystallographer Johannes Martin Bijvoet.

Occurrence and association

Bijvoetite- 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

Although originally thought to be orthorhombic, bijvoetite- was later shown to be monoclinic. The structural formula of the mineral is 14, where M =. The structure has 16 uranium sites, with uranium belonging to near-linear uranyl groups. The important features of the structure are:
  • presence of uranyl pentagonal bipyramids, formed by coordination of uranyl groups by three oxide and two hydroxyl anions
  • presence of uranyl hexagonal bipyramids, formed by coordination of another eight uranyl groups by six oxide anions
  • presence of uranyl carbonate chain parallel to, of a novel type, built of edge-sharing dimers of UPB and UHB, and carbonate groups
  • presence of irregular M3+Φn polyhedra linking the uranyl carbonate chain, thus forming a compound novel-type sheet parallel to
  • location of 14 water molecules in the interlayer space
  • bonding of the remaining 25 water molecules to trivalent cations