Letter: Octahedral cation distribution in palygorskite
-
Georgios D. Chryssikos
,
Vassilis Gionis
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, AlFe3+OH, Fe3+Fe3+OH) and trioctahedral-like (Mg3OH) species. Therefore, palygorskite can be approximated by the formula yMg5 Si8O20(OH)2·(1 - y)[xMg2Fe2·(1 - x)Mg2Al2] Si8O20(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/(VIAl + Fe) ratio from AEM (R2 = 0.98, σ = 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 (R2 = 0.90 and σ = 0.05) after calibrating the relative intensity of the Mg3OH vs. (Al,Fe)2OH overtone bands using AEM data. The agreement between the spectroscopic and analytical data are excellent. The data show that Fe3+ 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.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Amorphous materials: Properties, structure, and durability. The viscosity of hydrous NaAlSi3O8 and granitic melts: Configurational entropy models
- Alteration mineralogy and the effect of acid-leaching on the Pb-isotope systematics of ocean-island basalts
- Color origin and heat evidence of paleontological bones: Case study of blue and gray bones from San Josecito Cave, Mexico
- Coexistence of pyroxenes jadeite, omphacite, and diopside/hedenbergite in an albite-omphacite rock from a serpentinite mélange in the Kurosegawa Zone of Central Kyushu, Japan
- Amphibole equilibria in mantle rocks: Determining values of mantle aH2O and implications for mantle H2O contents
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- Dehydration dynamics of barrerite: An in situ synchrotron XRPD study
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- Dislocation modeling in calcium silicate perovskite based on the Peierls-Nabarro model
- Molecular dynamics insight into the cointercalation of hexadecyltrimethyl-ammonium and acetate ions into smectites
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- Letter: Octahedral cation distribution in palygorskite
