@article{fdi:010097121,
  title = {{O}ccurrence of 2:1 phyllosilicates in {F}erralsols : a viewpoint},
  author = {{B}ruand, {A}. and {B}rossard, {M}ichel and {C}aner, {L}.},
  editor = {},
  language = {{ENG}},
  abstract = {{I}n the humid tropics, {F}erralsols can be considered as being the end of a geochemical sequence of weathering. {E}asily weatherable primary minerals should then have completely disappeared; consequently, their fine fraction which is largely dominated by low-activity clay minerals, and aluminum and iron sesquioxides. {H}owever, the occurrence of small amounts of 2:1 phyllosilicates has been recorded in many {F}erralsols. {S}ince the presence of these minerals in these intensively weathered soils has never been the subject of a comprehensive study, we conducted an analysis of the literature from the past sixty years. {T}his has shown that, since the first studies, most of the 2:1 phyllosilicates recorded in {F}erralsols have been identified solely by {X}-ray diffraction, thanks to a peak at approximately 1.4 nm that did not expand upon solvation with ethylene glycol and became a broad peak between 1.2 and 1.0 nm when heated to 300 degrees {C}. {T}hese {XRD} features are similar to those observed for 2:1:1 phyllosilicates with incomplete {A}l-hydroxy interlayering. {T}he name given to these minerals has evolved over the years as knowledge about phyllosilicates advanced. {I}t was shown that these 2:1 phyllosilicates, often interpreted as hydroxy-{A}l interlayered minerals, were mainly present in the fine-silt and coarse-clay fraction. {T}hey were found in {F}erralsols of the {S}outh-{A}merican, {A}frican and {A}sian intertropical zones. {A}lthough their possible presence in very small proportions has gradually been integrated into the definition of {F}erralsols or equivalent soils according to the soil classification systems used, their origin remains debated. {W}hile some authors interpret them as resulting from neoformation processes within the soil or as being relict minerals that have resisted weathering processes, a growing number of authors interpret their presence, without calling into question the two previous hypotheses, as resulting from soil the mixing of by the by activity of social soil insects, in particular that of termites. {I}t is hypothesized that material transported from the saprolite seeded the entire {F}erralsol profile with 2:1 phyllosilicates, formed either through neogenesis or primary mineral weathering. {T}hese minerals remain observable today where soil fauna have redistributed them, and undergo aluminization and desilication consistent with the geochemical context to which they are exposed. {F}inally, studies on the availability of potassium potentially present in the interlayer space of the 2:1 phyllosilicates indicate that 5 to 30% of this potassium can be exchangeable when the {F}erralsols considered are still under native vegetation. {O}nce cultivated, this reserve of exchangeable potassium reserve is depleted within a few years, and subsequent annual inputs from the remaining potassium stock are very low.},
  keywords = {{T}ropical soil ; {F}errallitic soil ; {L}atosol ; {O}xisol ; {F}erralisol ; {F}errosol ; {F}errallisol ; {M}ica ; {I}llite ; {V}ermiculite ; {H}ydroxy-{A}l interlayered ; vermiculite ({HIV}) ; {S}mectite ; {H}ydroxy-{A}l interlayered smectite ({HIS}) ; {B}iological activity ; {T}ermite ; {ZONE} {TROPICALE}},
  booktitle = {},
  journal = {{G}eoderma},
  volume = {470},
  numero = {},
  pages = {117832 [17 p.]},
  ISSN = {0016-7061},
  year = {2026},
  DOI = {10.1016/j.geoderma.2026.117832},
  URL = {https://www.documentation.ird.fr/hor/fdi:010097121},
}