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The Red Latosols of Sri Lanka: II. Mineralogy and Weathering
Author(s) -
Alwis K. A.,
Pluth D. J.
Publication year - 1976
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/sssaj1976.03615995004000060032x
Subject(s) - kaolinite , weathering , mineralogy , clay minerals , vermiculite , hematite , geology , mica , mineral , muscovite , red soil , soil water , geochemistry , chemistry , quartz , soil science , paleontology , organic chemistry
Soil samples from the principal soil series of the Red Latosols of Sri Lanka were subjected to (i) mineralogical analysis of the fine sand fractions by density, magnetic and optical methods, and (ii) mineralogical analysis of the clay and silt fractions by X‐ray diffraction, DTA, chemical, and electron optical methods in order to characterize these soils and elucidate their genesis. Mineralogical analysis of the fine sand fractions confirmed that the parent materials were uniform with depth and within series, but differed among series. The near‐complete absence of easily weatherable minerals indicates intense weathering either before deposition or during soil formation. The fine (< 0.2 µm) clays of all three Red Latosol soil series consist almost exclusively of well‐crystallized kaolinite. The remainder is made up of free iron oxides and a small amount of amorphous components. Similarly the coarse (2–0.2 µm) clays are dominated by kaolinite, but they also contain minor amounts of other minerals, chiefly mica and mixed layer minerals with anatase and possibly some interstratified materials being present as traces. Coarse clays from the Wilpattu series contain, in addition, a clay mineral that is probably a vermiculite‐smectite intergrade. The mica in the surface horizons appears to be stabilized against weathering, possibly by phytocyling of K. Free iron oxides are present mainly as discrete particles of hematite. Small amounts of amorphous materials also occur.