Infrared evidence of dioctahedral-trioctahedral site occupancy in palygorskite

A Mg-rich palygorskite sample from phosphorite deposits of Ganntour (Morocco) with the structural formula Si-8(Mg(2.6)Al(1.19)Fe(0.33)(III)square(0.88))Ca0.056Na0.024K0.104O20(OH)(2)(OH2)(4).4H(2)O, was studied by FTIR spectroscopy. In both OH-stretching and OH-bending regions, there is evidence of dioctahedral Al(2)squareOH, AlFesquareOH and trioctahedral Mg3OH features, leading to a di-trioctahedral crystallochemical model of octahedral site occupancies in ribbons of Ganntour palygorskite. This model, established through the IR spectroscopy study of a Mg-rich palygorskite, seems to be appropriate for many other palygorskites with lower Mg content in the octahedral sheet.