Talc from Puebla de Lillo, Spain. I. XRD study

Abstract

Talc from Puebla de Lillo, Spain has been studied by XRD. The experimental X-ray powder diffraction patterns have been compared with simulated diffractograms from structure refinement data for the triclinic and monoclinic talcs. For differently oriented particles in aggregates ( g = 0, 1, 2, 3) a series of diffraction patterns of monoclinic and triclinic talcs were calculated. The results proved that the relative intensities are highly dependent on the g parameter, even for the very weakly textured samples. It has also been found that the texture modified relative intensities are evidently different for the two polytypic modifications. The polytypism of talc is discussed. The X-ray results were compared with those obtained for other talc samples (Turkey, Egypt). The unground sample of talc from Puebla de Lillo studied here belongs to fine grained steatite, characterized by disordered structure. Due to random translations of the layers along the Y axis all the reflections of the 02 l and 11 l series (which correspond with YZ projection) are smeared out. A ‘shape factor’ was found helpful in the identification of polytype if a coefficient of orientation has been measured independently. It displays lower values for the triclinic polytype than for the monoclinic one for the same g value. Talc from Puebla de Lillo was determined to belong to crystallographic subfamily A. Indication of its monoclinic symmetry was derived from the comparison of the experimental and calculated diffractograms and from the ‘shape factor’ determination.