Synthesis of ludwigite along the Mg2FeBO5 – Mg2AlBO5 join

bearing ludwigite on the Mg2(Al,Fe)BO5 - Mg 2AlBO5 join was synthesized in a standard externally-heated pressure vessel over a temperature range of 600-700 °C, with pressures of 500-1000 bar, for a period of three days. Four starting mixtures were used: (1) Mg2(Fe075Al025)BO 5, (2) Mg2(Fe05Al05)BO5, (3) Mg 2(Fe025Al075)BO5, and (4) Mg 2AlBO5. Products were examined by X-ray diffraction (XRPD) and electron microscopy with an energy-dispersive spectrometer (SEM/EDS). In these experimental conditions, single-phase Al-bearing ludwigite was only obtained at high temperature and pressure (700 °C, 1000 bar), since reactions were only partially completed at lower temperatures and pressures. The chemical composition of Al-bearing ludwigite was generally close to that of the starting materials, especially for those with lower aluminum content. Variations in cell parameters were nearly linear, as a function of composition. These results may improve our understanding of the varied occurrence of natural Al-rich ludwigite minerals.