Title page for ETD etd-02062013-040123
|Type of Document
||Synthesis and crystal chemistry of lanthanide allanites
|Hewitt, David A.
|Bloss, F. Donald
|Gibbs, Gerald V.
|Ribbe, Paul H.
|Speer, J. Alex
|Date of Defense
Metamictization and complex chemistry are major obstacles to the crystal chemical
characterization of natural allanites. To overcome these problems, allanites,
Ca(REE)Fe2+AlzSi3O12(OH), where REE = La, La-Ce, Ce, Nd, Sm, Eu, Gd, Er, Dy, Yb
and Y have been synthesized hydrothermally from unbuffered and buffered oxide mixes at
500 to 650°C, 5.5 kbar (550 MPa), and 700 to 725°C, 4 kbar (400 MPa). Although
allanite is readily synthesized, high yields are obtained only for allanite-(LREE)
compositions, and end—member composition is obtained only for allanite-(La). Er and Yb
ions are too small to substitute at the A(2) site in allanite, but a small amount can substitute
at the VI~coordinated M(3) site. Fe2+ in the M(3) site favors LREE substitution, which
supports the contention that allanite is Ce—selective.
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