Synthesis and crystal chemistry of lanthanide allanites

• Main Author: Affholter, Kathleen
• Other Authors: Geological Sciences
• Format: Others
• Language: en
• Published: Virginia Tech 2014
• Subjects: LD5655.V856 1987.A335; Allanite
• Online Access: http://hdl.handle.net/10919/37332; http://scholar.lib.vt.edu/theses/available/etd-02062013-040123/

Metamictization and complex chemistry are major obstacles to the crystal chemical characterization of natural allanites. To overcome these problems, allanites, Ca(REE)Fe²+Al₂Si₃O₁₂(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. === Ph. D.