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Soil Science Society of America Journal Abstract -

Characterization of Mineral Forms in Andepts from Chile1


This article in SSSAJ

  1. Vol. 39 No. 3, p. 556-561
    Received: Apr 24, 1974
    Accepted: Feb 17, 1975

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  1. W. Espinoza,
  2. R. H. Rust and
  3. R. S. Adams Jr.2



The mineralogy of two undisturbed volcanic soils from Chile (Typic Dystrandepts) and of the sand and clay-size particles of the soil residues was studied by using ultrasonic, scanning electron microscope, X-ray diffraction, transmission electron microscope, infrared spectroscopy, differential thermal analysis, and electron microprobe techniques. The effects of removal of organic matter, free iron and aluminum oxides, and amorphous alumino-silicates was evaluated in the X-ray, DTA, and IR analyses. The soils are characterized by an amorphous inorganic matrix in a flocculated state with a sponge type structure. This matrix presents a high specific surface (225 m2/g), CEC of about 45 meq/100g at pH 7.0, low base saturation (< 20%) and bulk density of 0.9 to 1.1 (g/cm3) and SiO2/Al2O3 molar ratio of 2.0 to 4.0. Organic matter appeared in some well preserved structures, partially due to silica accumulation. The principal primary minerals are fresh volcanic glass and K-feldspars and the principal secondary mineral is allophane or an amorphous analog. The removal of organic matter, free iron and aluminum oxides and amorphous alumino-silicates did not alter the DTA, X-ray and IR patterns.

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