Biomineralization in Bauxitic Laterites of Modern and Paleotropics of Earth

Abstract

The top part of a lateritic profile including laterites in sensu stricto, bauxites and even zones of clay minerals (кaolinite, halloysite, montmorillonite), contains plentiful traces and products of interaction of a substratum with live organic substance and mortmasses. The surface of laterites is hidden under the cover of trees and bushes and the dense felt like a film weaved from filamentous fungus, roots of vegetation, and fossilized microorganisms. Dying off, they turned into biofilms, which is replaced with biominerals such as gibbsite-Al (OH)₃, goethite-HFeO₂, hematite-α-Fe₂O₃, and halloysite-Al₄(OH)₁₀[Si₄O₈](OH)₂ · 4H₂O. A zone of a biological pedoturbation is completely processed by the burrowing organisms. Earlier it was represented that they make only mechanical impact on rocks. We revealed that burrowing organisms, including worms, mill all minerals of a substratum, passing it through the digestive path, and satiate it with biochemically active substances. It causes dissolution of all minerals except rutile—TiO₂. Gibbsite, when passed through a digestive path, recrystallizes and forms surprisingly beautiful and perfect idiomorphic crystals filling the burrows of the worms and covering their walls. We managed to find the paradoxical phenomenon: passing of worms through large (2–4 cm) quartz crystals. The entrances are surrounded with a biofilm similar to slimes and turned into units of crystals of hematite. The described phenomena are established on numerous bauxite deposits of India, Guinea, and Brazil of the modern tropic and on the ancient deposits of Siberia.