Synthesis of REE and Y phosphates by Pb-free flux methods and their utilization as standards for electron microprobe analysis and in design of monazite chemical U-Th-Pb dating protocol

(REE,Y) phosphates were synthesized in a 1 atm furnace by ß ux-growth methods involving Pb-free ß uxes. Microcrystalline (REE,Y) phosphate was precipitated from a solution of (REE,Y) chlorides or nitrates plus ammonium dihydrogen phosphate, and mixed with a M2CO3 (M = Li or Na)-MoO3 flux (75:25:2 molar ratio M2CO3:MoO3:REEPO4). Crystal growth was achieved over the temperature range 1350.870 °C, with extended (15 h) high-T soaking, and cooling rates of 3 °C/h. Crystals grown by this method are clear, generally inclusion-free, up to several mm in length, and are easily extracted from the water-soluble flux. Crystal size and habit are influenced by the alkali component of the flux. Successful LREE phosphate synthesis is favored by both Li-and Na-bearing fluxes, whereas better results for Y and MREE-HREE phosphates were achieved with Na-bearing fluxes. Li-bearing fluxes produced LREE phosphates with an overall platy habit, in contrast to more prismatic-to-equant LREEMREE phosphates produced with Na-bearing fluxes.