Palygorskite From Bolca, Italy - A Characterization By High-resolution Synchrotron-radiation Powder Diffraction and Computer Modeling

A new find of the mineral palygorskite from Bolca, Vicenza, Italy is described. The mineral occurs in association with calcite and diaspore along the shear fractures and in the veins of secondary minerals in the Eocene marls of the Bolca quarry, a locality known for its well-preserved fossil specimens. Selected regions of the X-ray powder diffraction spectra (XRPD) were collected using X-ray synchrotron radiation and high-resolution parallel-beam geometry. The data are interpreted by comparison with the computer-simulated powder diffraction patterns relative to the proposed strcture models for palygorskite. Cell parameters and relative phase weight evaluation were obtained by model-constrained Rietveld refinement. The sample was also investigated by electron probe micro-analysis (EPMA), TGA and DTG analysis, and SEM imaging. The average material is a mixture containing about 60% orthorhombic palygorskite, 30 % monoclinic palygorskite, and less than 10 % calcite and diaspore impurities. The association of the two different varieties of palygorskite is in agreement with recent re-evaluation studies of the mineral from different localities, showing the ubiquitous presence of the two forms.