Letter: Octahedral cation distribution in palygorskite
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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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Artikel in diesem Heft
- 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
- Experimental fluoridation of nanocrystalline apatite
- Dehydration dynamics of barrerite: An in situ synchrotron XRPD study
- Structural features in Tutton’s salts K2[M2+(H2O)6](SO4)2, with M2+ = Mg, Fe, Co, Ni, Cu, and Zn
- Incorporation of water in iron-free ringwoodite: A first-principles study
- Temperature dependence of reflectance spectra and color values of hematite by in situ, high-temperature visible micro-spectroscopy
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- Solubility of H2O and CO2 in ultrapotassic melts at 1200 and 1250 °C and pressure from 50 to 500 MPa
- Multi-analytical approach to solve the puzzle of an allanite-subgroup mineral from Kesebol, Västra Götaland, Sweden
- 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
- Adding further complexity to the polybasite structure: The role of Ag in the B layer of the -M2a2b2c polytype
- Structural position of H2O molecules and hydrogen bonding in anomalous 11 Å tobermorite
- Electronic structures of siderite (FeCO3) and rhodochrosite (MnCO3): Oxygen K-edge spectroscopy and hybrid density functional theory
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- The composition of KLB-1 peridotite
- Crystal chemistry of the magnetite-ulvöspinel series
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- Letter: Octahedral cation distribution in palygorskite
