TY - JOUR ID - 10442/12705 A1 - Chryssikos, G. D. A1 - A1 - Gionis, V. A1 - A1 - Kacandes, G. H. A1 - A1 - Stathopoulou, E. T. A1 - A1 - Suarez, M. A1 - A1 - Garcia-Romero, E. A1 - A1 - del Rio, M. S. Y1 - 2009/// T1 - Octahedral cation distribution in palygorskite JF - American Mineralogist VL - 94 IS - 1 SN - 0003-004X U3 - 10.2138/am.2009.3063 PB - Mineralogical Society of America SP - 200–203EP - UR - https://hdl.handle.net/10442/12705 N2 - The OH speciation of 18 palygorskite samples from various localities were evaluated by near infrared spectroscopy (NIR) and compared to the corresponding octahedral composition derived from independent, single-particle analytical electron microscopy (AEM). NIR gives evidence for dioctahedral-like (AlAlOH, AlFe(3+)OH, Fe(3+)Fe(3+)OH) and trioctahedral-like (Mg(3)OH) species. Therefore, palygorskite can be approximated by the formula yMg(5) Si(8)O(20)(OH)(2).(1 - y)[xMg(2)Fe(2).(1-x)Mg(2)Al(2)] Si(8)O(20)(OH)(2), where x is the Fe content of the dioctahedral component, and y is the trioctahedral fraction. The values of x estimated from the NIR data are in excellent agreement with the Fe/((VI)Al + Fe) ratio from AEM (R(2) = 0.98, sigma = 0.03), thus suggesting that all octahedral Al and Fe in palygorskite participate in M2M2OH (dioctahedral-like) arrangements. furthermore, y values from AEM can be compared to NIR (R(2) = 0.90 and sigma = 0.05) after calibrating the relative intensity of the Mg(3)OH vs. (Al,Fe)(2)OH overtone bands using AEM data. The agreement between the spectroscopic and analytical data are excellent. The data show that Fe(3+) for Al substitution varies continuously in the analyzed samples over a broad range (0