ABSTRACT A boule of blue spinel, produced following the Veneuil technique, was characterized under the chemical and crystallographic points of view. The average chemical formula, calculated from several hundred EDS analyses, results: Mg0.380 Al2.410O4, but important fluctuations in the Mg-Al content from point to point were detected. The crystallographic constant, obtained from X-ray powder method, is a0 =7.9732 Å. Slices of the boule, cut with different orientations with respect to the elongation axis, studied by optical microscopy and by X-ray transmission topography, Lang method, showed domains misoriented by small angles. The development of the different domains during the growth of the sample may explain the optical and topographic behaviours. The optical figures observed under the polarizing microscope on the different slices were related to the optical contrasts showed by the cut stones used for gemmological applications.
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