Gibbsite and kaolinite in the biological pedoturbation zone of the lateritic profile: A different fate (exemplified by deposits of Siberia, India, Guinea, and Brazil)

Biofilms and Biominerals in the Lateritic Weathering Crust as Exemplified by the Central Bauxite Deposit (Siberian Platform, Russia)

“…Type I composition is Al and Al 0.93 Si 0.05 , and type II is Al 0.94 Si 0.05 . In the patterns of the first type, relatively weak reflexes hk0 with h + k = 2n + 1 corresponding to a monoclinic structure (spatial group P2 1 /n) were observed, while in the patterns of the second type, these reflexes caused by monoclinic distortion of perfect trigonal gibbsite structure were absent, with reflexes hk0 with h + k = 2n more blurred in comparison than these reflexes in electronograms of the first type [3]. The appearance in some electronograms of the first type of h00 reflexes with 0k0 odd values of h or k indices forbidden by the spatial group P2 1 /n is likely connected with a local symmetry breaking of gibbsite crystals.…”

“…The appearance in some electronograms of the first type of h00 reflexes with 0k0 odd values of h or k indices forbidden by the spatial group P2 1 /n is likely connected with a local symmetry breaking of gibbsite crystals. In the patterns from textured gibbsite polycrystals, the hk0 reflexes with h + k = 2n + 1 were not observed [3,[15][16][17]. A common feature of gibbsite is an irregular, often smooth shape of particles up to 2 microns in size.…”

“…They form on any wet surface in the weathered rock strata, in cracks, pores, and caverns, penetrate deep after the filtered water, and are fixed at the top of the profile by evapotranspiration. Biofilms are especially abundant in the zone of biopedoturbation, where swarming organisms, supplying bauxite, are the most active biochemical substances [3].…”