Cation Exchange Capacity of Layer Silicates and Palagonitized Glass in Mafic Volcanic Rocks: A Comparative Study of Bulk Extraction and In Situ Techniques

Abstract

Abstract--The cation exchange capacities (CEC) and extractable cations in smectite, corrensite and palagonitized glass from hydrothermally-altered pillow lavas and hyaloclastite breccias were measured by both bulk wet chemical and in situ microanalytical techniques. Smectite has CEC's between 60 and 120 meq/100 g, palagonitized glass between 30 and 60 meq/100 g, and corrensite approximately 35 meq/100 g as determined by the in situ CsCl-exchange method. These experiments generally verify that Cs exchanges for those cations that are presumed (from the stoichiometry implied by microprobe analyses) to occupy interlayer sites in sheet silicates. Results of conventional CEC determinations are consistent with those determined by the in situ experiments: the individual microanalytical values for smectite and palagonitized glass bracket the bulk CEC values. The in situ experiments imply that Mg is the major extractable cation in smectite, Ca in corrensite, and both Mg and Ca in the palagonitized glass. We speculate that discrepancies between the equivalents of extractable cations predicted from elemental analysis and the equivalents of Cs sorbed may be due to the presence of charge-balancing protons that are not detected by the microprobe analyses. The sum of equivalents of cations extracted by NH~-acetate is about the same as the CEC determined by both the in situ and the bulk methods. Cation proportions indicated by NH4-acetate extractions from bulk samples are also generally consistent with the in situ results for all elements except Mg, which is a minor leachate of the NH4-acetate extractions in all the samples. To explain this discrepancy, we propose that l) Mg may occupy structural sites within palagonitized glass, which inhibit its extraction by NH 4 or Cs, and/or 2) there is a significant quantity of smectite, unsampled by the electron microprobe analyses, which contains insignificant interlayer Mg.

Experimental Clay-Mineral Formation from a Subvolcanic Rock by Interaction with 1 M NaOH Solution at Room Temperature

“…Christidis (1989) found that in the Garyfalakena deposits, Mg occupies ~70% of the exchangeable sites. Also, Schiffman and Southard (1996) measured the cation-exchange capacity and extractable cations of smectite with both traditional bulk methods and an in situ method using the electron mi- croprobe. They found that the in situ method implies that Mg is the major extractable cation in this smectite.…”

Reduction of nitrogen compounds in oceanic basement and its implications for HCN formation and abiotic organic synthesis

“…smectites, double layer hydroxides) and zeolites [4-6]. Zeolites like phillipsite coexist with smectite and almost always with mafic glass [7].…”

Methods forIn SituSIMS Microanalysis of Boron and its Isotopes in Palagonite

“…The electron-beam settings were 15 KeV accelerating voltage with 2 nA regulated current, and the beam was rastered over a 5 mm 65 mm area. Peaks and backgrounds were typically counted for 10 s. Net intensities relative to oxide and silicate calibration standards were converted to concentrations using standard ZAF correction techniques (Schiffman and Roeske, 2002). Accuracy was evaluated by analyzing working reference standards as unknowns under the same analytical conditions.…”

“…According to Zhang et al (1998) and Williams and Hervig (2005) adsorbed B could can be removed from exchangeable sites of bulk smectite separates using a concentrated 1 M NH 4 Cl solution. Using major-element composition as analyzed by EPMA, Schiffman and Southard (1996) showed that cations can be exchanged in thin-section samples of both smectite and palagonite using a CsCl solution. As part of the present study, an experiment was performed on palagonite thin sections to determine if adsorbed B can be removed from exchangeable sites of the sample using NH 4 Cl solution.…”