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The Origin of Vermiculite in Soils Developed from Lower Palaeozoic Sedimentary Rocks in Mid‐Wales
Author(s) -
Adams W. A.,
Kassim J. K.
Publication year - 1983
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1983.03615995004700020029x
Subject(s) - vermiculite , illite , chlorite , soil water , clay minerals , geology , sedimentary rock , geochemistry , paleozoic , mineralogy , chemistry , soil science , paleontology , quartz
Vermiculite occurs frequently in mid‐Wales' soils derived from Lower Palaeozoic sedimentary rocks though illite and chlorite are the only clay minerals in the parent rock. Vermiculites were produced experimentally from rock illite by fusion with LiNO 3 and from chlorite by oxidation at 400°C in the presence of Na 2 Cr 2 O 7 . The proportion of vermiculite in illitic clay treated with LiNO 3 was closely correlated with K or Na content whereas no such relationship was apparent in soil clays which contained vermiculite. The cation exchange capacity (CEC) of experimentally altered illite was closely correlated with vermiculite content and although the CEC of soil clays was also correlated with vermiculite content the relationships were quite different. The susceptibility to chemical dissolution of soil vermiculite was found to be more akin to that of vermiculite produced from chlorite than vermiculite derived from illite. A positive relationship was found between the vermiculite content of soil clays and total free iron content. Vermiculite was low or absent from highly weathered, gleyed eluvial horizons of stagnopodzols. Laboratory and field evidence support the conclusion that the vermiculite which occurs in the relatively young soils examined is predominantly a product of chlorite alteration under aerobic conditions. The evidence suggests that there has not been a significant alteration of illite to vermiculite in soils developed in postglacial deposits.