This metadata file gathers crystal-chemical, crystallographic and spectroscopic raw data supporting the manuscript entitled “Niobium speciation in minerals revealed by L2,3-edges XANES spectroscopy“ submitted to American Mineralogist. EMP_natural_references: spreadsheet compiling crystal-chemical data of the Nb geological references (columbite, fluorcalciopyrochlore, hydropyrochlore, latrappite, niocalite) obtained from electron microprobe analysis (EMP_crystal_chemistry_references.xls). Analyses were conducted on a CAMECA SX Five electron at the CAMPARIS facility (Sorbonne Universite, Paris). Two to seven spots were probed for each sample at 15 kV and 40 nA for the major elements and at 15 kV and 299 nA for minor and : trace elements. WDS analyses were performed using the following standards: albite for Na, diopside for Mg, Si and Ca, orthoclase for Al and K, MnTiO3 for Mn and Ti, hematite for Fe, BaSO4 for Ba; topaze for F, LiNbO3 for Nb, metallic Ta for Ta, SrSi for Sr, zircon for Zr, galena for Pb, monazite for Th, uraninite for U, and REE-bearing silicates for for Y, La, Ce, Nd. XANES_spectra: raw X-ray absorption data files (.dat). There are either one or two files per sample (_01/_02). Amounts of Nb in Ti oxide samples are mentionned in file titles (Nb1pc/Nb5pc/Nb10pc). Niobium L2,3-edges XANES spectra were recorded on the LUCIA beamline of the SOLEIL synchrotron radiation facility (Gif-sur-Yvette, France) operating with a storage ring current of 450 mA and energy of 2.75 GeV. A double crystal Si(111) monochromator crystal was used with an energy resolution of 0.25 eV at 2400 eV and calibrated at this energy using Nb2O5. XRD_geological_references: spreadsheet compiling crystal-cell parameters obtained from the reduction of single-crystal XRD data (geological_samples_crystal_cell_data.xls). The number of reflections indexed and teta range of measurement are specified. An Agilent Diffraction Xcalibur-S diffractometer equipped with a Sapphire CCD-detector with Mo K-α1 radiation (λ = 0.71073 Å, graphite monochromator) was used at room temperature. Data reduction, cell refinement and space group determination were performed using CrysAlisPro software. XRD_synthetic_samples: XRD data obtained for the synthetic samples (.csv/.xrdml). Amounts of Nb in Ti oxide samples are mentionned in file titles (Nb1pc/Nb5pc/Nb10pc). X-ray diffraction was performed with a PANALYTICAL X’pert Pro MPD diffractometer. Measurements were carried out in Bragg-Brentano geometry using a Co K-α anode in order to minimize the X-ray absorption of Fe in iron oxide synthetic compounds. Data were recorded with an X’Celerator detector between 3 ° 2θ and 90 ° 2θ with 0.017 ° steps. Incident beam mask was fixed at 20 mm and soller slits at 0.04 rad.