An Apatite-Group Praseodymium Carbonate Fluoroxybritholite: Hydrothermal Synthesis, Crystal Structure, and Implications for Natural and Synthetic Britholites
Michael Anenburg, Taras L. Panikorovskii, Eleanor S. Jennings, Roman Shendrik, Andrey A. Antonov, Veronika Gavrilenko
Abstract
High Resolution Image Download MS PowerPoint Slide Britholites are the lanthanide–silica-rich end-members of the apatite group, commonly studied for their optical properties. Here, we show ∼50–100 μm single crystals synthesized hydrothermally at 650–500 °C and 500–300 MPa composed of a solid solution between Ca 2 Pr 3 (SiO 4 ) 3 F–fluorbritholite and CaPr 4 (SiO 4 ) 3 O–oxybritholite, with a significant carbonate component substitution, via C 4+ replacing Si 4+ . Single-crystal X-ray diffraction and density functional theory computations show that a planar carbonate group occupies the face of a now-vacant silica tetrahedron. This modifies Pr–O bond lengths, diversifying lanthanide optical emission wavelengths. Our britholite was synthesized in geologically reasonable conditions and compositions, suggesting that carbonated oxybritholites could exist as yet-unrecognized natural minerals.