THE REDEFINITION OF TENGERITE-(Y), Y2(CO3)3.2-3H2O, AND ITS CRYSTAL-STRUCTURE

Tengerite-(Y) is redefined as a hydrous yttrium carbonate mineral with an ideal formula Y2(CO3)3.nH2O (n = 2-3), on the basis of reexaminati on of the type specimen, type locality specimens, and synthetic sample s. Ca, although previously reported in the literature, is found not to be an essential component of tengerite-(Y). Tengerite-(Y) is orthorho mbic, with space group Bb2(1)m. The crystal structure of tengerite-(Y) was solved and refined to R = 0.045 for 765 independent reflections u sing a hydrothermally synthesized single crystal. Refined lattice para meters are a = 6.078(4), b = 9.157(2), and c = 15.114(6) angstrom, Z = 4. The structure can be described as a sheet structure built up from ninefold-coordinated Y polyhedra and CO3 trigonal planar groups. The c orrugated sheets are connected by other CO3 groups to form a three-dim ensional framework. The structure of tengerite-(Y) is not related to t hat of lanthanite-(La) despite their compositional similarity. It is s uggested that tengerite-(Y) has a close structural relationship to kim uraite-(Y) and lokkaite-(Y), whereas lanthanite-(La) is related to cal kinsite-(Ce).