L'altération latéritique débutante des pyroxénites de Jacuba, Niquelandia, Brésil

International audienceThe initial weathering products under lateritic conditions of orthopyroxenes and clinopyroxenes in Jacuba, Niquelandia, Brasil, are amorphous and have chemical compositions very near those of the parent minerals but with enrichment of Ni. Later products are phyllosilicates such as talc, saponite and pimelite, the nature and composition of which vary with the development of porosity and fissuring of the parent rock. It appears that Ni distribution between these phyllosilicates is also controlled by fissure development. As the parent pyroxenes are Ni-depleted, it is clear that Ni accumulation in the structures of the phyllosilicate weathering products is a result of solution transfer from other parts of the profile.L'alteration lateritique débutante des orthopyroxenes et clinopyrox6nes de Niquelandia, Bresil, montre plusieurs stades. Le premier stade facultatif est la formation de produits 'amorphes" dont la composition chimique proche de celle des min~raux parentaux, montre d6j~i un enrichissement en nickel. Le deuxième stade est marqué par l'apparition de phyllosilicates dont la nature et la composition chimique varient scion le degré de porosité de la roche parentale. Cette porosité contrôle également la distribution du nickel dans les différents phyllosilicates, (saponite, talc, pimelite). Les pyroxènes ne contenant pas ou tr6s peu de nickel, il est clair que le nickel qui s'accumule dans les produits de l'altération est totalement importé avec les eaux de percolation. L'origine de ce nickel est fi rechercher plus haut dans les profils ou plus en amont dans la séquence, là ou les dunites sont présentes

Hormesis: why it is important to biogerontologists

This paper offers a broad assessment of the hormetic dose response and its relevance to biogerontology. The paper provides detailed background information on the historical foundations of hormesis, its quantitative features, mechanistic foundations, as well as how the hormesis concept could be further applied in the development of new therapeutic advances in the treatment of age-related diseases. The concept of hormesis has direct application to biogerontology not only affecting the quality of the aging process but also experimental attempts to extend longevity