Clay minerals of two Eutrandepts of Hawaii, having isohyperthermic temperature and ustic moisture regimes
Wada, K. | Kakuto, Y. | Ikawa, H.
Clay minerals of two pedons of Naalehu soils from Hawaii were studied by a combination of methods. According to Soil Taxonomy, they are classified as medial, isohyperthermic Typic Eutrandept. In the Andisol proposal, Naalehu-1 is not an Andisol because its P retention is <85%, but Naalehu-2 is classified as an Andisol because it meets all of the definitions of andic materials. Their clay content was high (49-85%), with no significant difference between the two soils. The Naalehu-2 soil clays, however, had higher contents of oxalate-oxalic acid soluble aluminosilicates and Fe oxides than the Naalehu-1 soil clays. These clays also showed halloysite (1.0 nm), concentric spherules and curled flakes, and possibly hollow spherical aluminosilicates having a close structural relation with allophane. The Naalehu-1 soil clays, on the other hand, showed smectite, halloysite (1.0 nm), and their interstratified species. Both soils contained X-ray-detectable amorphous Fe oxides in the clay and poorly crystalline maghemite, olivine, and plagioclase in the silt and sand fractions. The importance of the soil-forming factors of parent material, climate (soil moisture and soil temperature), and age was inferred from comparison of the smectite and/or hilloysite mineralogy of the isohyperthermic Naalehu soils with the imogolite and/or or allophane mineralogy of the isothermic and isomesic Maui soils studied earlier.
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