title: Low-magnesium uranium-calcite with high degree of crystallinity and gigantic luminescence emission.
abstract: Cabrera (Madrid) low-Mg calcites exhibit: (i) an unusual twofold elevation in X-ray diffraction pattern intensity; (ii) a 60-fold elevation of luminescence emission, compared to six common natural calcites selected for comparison purposes; (iii) a natural relatively high radiation level of circa 200 nSvh(-1) not detected in 1300 other calcites from the Natural History Museum of Madrid. Calcites were analysed by the X-ray diffraction powder method (XRD), cathodo-luminescence spectroscopy in scanning electron microscopy (CL-SEM), thermoluminescence (TL), differential thermal analysis (DTA), X-ray fluorescence spectrometry (XRF) and particle size distribution (PSD). The Cabrera calcite study shows: (i) helicoidally distributed steps along the (0001) orientation; (ii) protuberance defects onto the (0001) surface, observed by SEM; (iii) XRF chemical contents of 0.03% MgO, 0.013% of Y(2)O(3), and 0.022% of U(3)O(8), with accessory amounts of rare earth elements (REE); (iv) DTA dissociation temperature of 879 degrees C; (v) TL maxima peaks at 233 and 297 degrees C whose areas are 60 times compared to other calcites; (vi) spectra CL-SEM bands at 2.0 and 3.4 eV in the classic structure of Mn(2+) activators; (vii) a twofold XRD pattern explained given that sample is a low-Mg calcite. The huge TL and CL emissions of the Cabrera calcite sample must be linked with the uranyl group presence. This intense XRD pattern in low-Mg calcites could bring into being analytical errors.
authors.affiliation: Instituto de Cerámica y Vidrio, CSIC, Cantoblanco, 28049 Madrid, Spain.
authors.forename: Francisco-Jose
authors.initials: FJ
authors.lastname: Valle-Fuentes
authors.forename: Javier
authors.initials: J
authors.lastname: Garcia-Guinea
authors.forename: Ana
authors.initials: A
authors.lastname: Cremades
authors.forename: Virgilio
authors.initials: V
authors.lastname: Correcher
authors.forename: Sergio
authors.initials: S
authors.lastname: Sanchez-Moral
authors.forename: Rafael
authors.initials: R
authors.lastname: Gonzalez-Martin
authors.forename: Luis
authors.initials: L
authors.lastname: Sanchez-Muñoz
authors.forename: Paula
authors.initials: P
authors.lastname: Lopez-Arce
mesh_terms: D002119:Calcium Carbonate / Q000032:analysis* / Q000737:chemistry*; D003460:Crystallization; D006207:Half-Life; D008163:Luminescent Measurements / Q000379:methods*; D008274:Magnesium / Q000032:analysis* / Q000737:chemistry; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D014501:Uranium / Q000032:analysis* / Q000737:chemistry*
chemical_list: D014501:Uranium; D002119:Calcium Carbonate; D008274:Magnesium