Crystal Structure Refinements of Four Monazite Samples from Different Localities

• Main Authors: M. Mashrur Zaman, Sytle M. Antao
• Format: Article
• Language: English
• Published: MDPI AG 2020-11-01
• Series: Minerals
• Subjects: monazite; crystal structure; chemical analysis; structural variations
• Online Access: https://www.mdpi.com/2075-163X/10/11/1028

This study investigates the crystal chemistry of monazite (<i>A</i>PO₄, where <i>A</i> = Lanthanides = Ln, as well as Y, Th, U, Ca, and Pb) based on four samples from different localities using single-crystal X-ray diffraction and electron-probe microanalysis. The crystal structure of all four samples are well refined, as indicated by their refinement statistics. Relatively large unit-cell parameters (<i>a</i> = 6.7640(5), <i>b</i> = 6.9850(4), <i>c</i> = 6.4500(3) Å, <i>β</i> = 103.584(2)°, and <i>V</i> = 296.22(3) ų) are obtained for a detrital monazite-Ce from Cox’s Bazar, Bangladesh. Sm-rich monazite from Gunnison County, Colorado, USA, has smaller unit-cell parameters (<i>a</i> = 6.7010(4), <i>b</i> = 6.9080(4), <i>c</i> = 6.4300(4) Å, <i>β</i> = 103.817(3)°, and <i>V</i> = 289.04(3) ų). The <i>a</i>, <i>b</i>, and <i>c</i> unit-cell parameters vary linearly with the unit-cell volume, <i>V</i>. The change in the <i>a</i> parameter is large (0.2 Å) and is related to the type of cations occupying the <i>A</i> site. The average <<i>A</i>-O> distances vary linearly with <i>V</i>, whereas the average <P-O> distances are nearly constant because the PO₄ group is a rigid tetrahedron.