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|Title:||Octahedral cation distribution in palygorskite|
|Author/Creator:||Chryssikos, Georgios D.|
Kacandes, George H.
Stathopoulou, Elizabeth T.
del Rio, Manuel Sanchez
|Type:||Journal Article (Scientific Journal article)|
|Abstract:||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 <x < 0.7), suggesting that fully ferric dioctahedral palygorskites (x = 1) may exist. On the other hand, the observed upper trioctahedral limit of y= 0.50 calls for the detailed structural comparison of Mg-rich palygorskite with sepiolite.|
|Publisher:||Mineralogical Society of America|
|Journal Title:||American Mineralogist|
|Keywords:||Palygorskite; Fe-rich; Mg-rich; structure; near infrared spectroscopy; trioctahedral; dioctahedral; composition; AEM; sepiolite; Geochemistry & Geophysics; Mineralogy|
|Other Identifiers:||DOI: http://dx.doi.org/10.2138/am.2009.3063|
|Journal web Location :||http://www.minsocam.org/MSA/AmMin/AmMineral.html|
|Rights holder:||© MINERALOGICAL SOC AMER|
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