Formation of aluminium hydroxy vermiculite (intergrade) and smectite from mica under acidic conditions

Abstract

Aluminous hydroxy 2/1 clay minerals (‘intergrades’) can form in two ways: Al can either come externally from the solution, or internally from the mineral itself (octahedral or tetrahedral layers). This study is more concerned with the latter which seems the main source in acid soils.The most common organic acids present under natural conditions were used on two trioctahedral micas (phlogopite and biotite), and their chemical and mineralogical weathering effects were determined.Different kinds of mineralogical evolution are possible: mineral destruction by a few very complexing acids, possibly with intermediate stages (interstratified minerals); formation of ‘transformation’ smectite by acids derived from sugars; Al-hydroxy vermiculite formation (the 14 Å diffraction peak of which is stable under K saturation and vacuum). This evolution is the most frequent and is produced by the most numerous organic acids (even CO2), the acidity of which results in Al migration in the interlayer, but the complexing ability of which is not sufficient for Al removal.

Chlorite Vermiculitization and Pyroxene Etching in an Aeolian Periglacial Sand Dune, Allen County, Indiana

“…In the dune, the hydroxy-A1 vermiculite occurs nearest the surface, which is consistent with the dominant role played by carbonic acid in this sandy, organicpoor sediment (Vicente et al 1977). The transition from hydroxy-A1 vermiculite to vermiculite occurs at 64 cm depth.…”

“…Acidic conditions tend to favor the development of hydroxy-A1 interlayers in the vermiculites from surface horizons (Douglas, 1977), but there are exceptions to the rule that are sometimes explained by the type of acid that dominates the weathering solution (Vicente et aL, 1977). For example, vermiculite forms in the A horizon at the same time hydroxy-A1 vermiculite forms in the deeper B horizons of certain Adirondack soils (April et aL, 1986).…”

“…For example, vermiculite forms in the A horizon at the same time hydroxy-A1 vermiculite forms in the deeper B horizons of certain Adirondack soils (April et aL, 1986). This distribution can be explained by the presence of organic acids (especially citric and oxalic acids formed under aerobic conditions) from the overlying leaf-litter that prevent the formation of hydroxy-Al interlayers in the vermiculites at near-surface depths (Vicente et aL, 1977;April et aL, 1986).…”

Clay minerals from Weichselian glaciolimnic sediments of the Sępopolska Plain (NE Poland)

“…The lack of effects of post-sedimentary processes was confirmed by a poor acidity of the investigated material, which does not promote the development of vermiculite layers. These minerals are formed over the process of the leaching of alkaline ions at much lower pH (4-5) (Vincente et al 1977;Katarhansis 1988;Matsue & Wada 1989). Another reason that these minerals did not occur in glaciolimnic sediments was a lack of oxidoreductive conditions, necessary for their creation because these conditions provide the Fe 3+ ions composing them (Vincente et al 1977;Douglas 1989).…”

“…These minerals are formed over the process of the leaching of alkaline ions at much lower pH (4-5) (Vincente et al 1977;Katarhansis 1988;Matsue & Wada 1989). Another reason that these minerals did not occur in glaciolimnic sediments was a lack of oxidoreductive conditions, necessary for their creation because these conditions provide the Fe 3+ ions composing them (Vincente et al 1977;Douglas 1989). That is why mixed-layer minerals containing vermiculite layers found in the clay fraction of the glaciolimnic deposits under study could be chlorited vermiculites developed during weathering of biotite in the sequence biotite → vermiculite → chlorited vermiculite (Barnhisel & Bertschel 1989) or minerals of the chlorite/vermiculite type could be an intermediate product in the transformation of detrite chlorites to smectites (Senkayi et al 1981).…”