Crystallography of oriented magnetite inclusions in apatite

In this study, natural apatite containing fine-grained magnetite inclusions with welldeveloped shape-preferred orientation is investigated.These inclusions are aligned in trails parallel to the hexagonal prism facets and elongated along the c-axis of apatite.Electron probe microanalysis (EPMA) reveals a chemically homogeneous apatite, while Energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy identify these inclusions as magnetite.Carbonate-bearing inclusions, including calcite and gas-liquid inclusions with CO, N, and dissolved carbonate ions, are also observed.Calcite inclusions likely indicate carbonatitic magma during apatite growth, whereas gas-liquid inclusions suggest later hydrothermal alteration.Optical microscopy reveals three shape-preferred orientation (SPO) groups of lamellar magnetite inclusions, each elongated parallel to <0001> Ap and to one of the three <1120> Ap directions.Electron backscatter diffraction (EBSD) analysis defines a consistent axial relationship of <0001> Ap //<110> Mag across all inclusions.Additionally, inclusions following the three SPO directions exhibit distinct but symmetrically related planar relationships, reflecting two specific crystallographic orientation relationships (CORs).COR-1: one of the {1120} Ap planes parallel to one of the {411} Mag planes, and one of the {1010} Ap planes parallel to one of the {211} Mag planes.This COR is expressed in direction 1 and 3 as two equivalent variants.COR-2: one of the {1120} Ap planes parallel to one of the {211} Mag planes, and one of the {1010} Ap planes parallel to one of the {411} Mag planes.