The Formation of Iron Bearing Aluminosilicates

In 1966 the formation of aluminosilicates in marine environments was hypothesized by Mackenzie and Garrels (1966) who pointed out the potential significance of this process with respect to the oceanic chemistry and for global elemental cycles. As elements are transferred into solid phase and thus become insoluble this process is referred to reverse weathering . Within the scope of this textbook only a brief overview of the major processes and conditions of formation is intended to be outlined. 

Four major pathways for the formation of iron bearing aluminosilicates can be distinguished  

Formation from weathered basalt and volcanic ashes 

The first two pathways of formation will not be discussed here as they were found to be only of local/regional importance and are not eonsidered to be of major importance for early diagenetic reactions. Iron bearing clay mineral formation under high-temperatnre conditions near a hydro-thermal system of the Red Sea was studied by Bischoff (1972). A direct precipitation of an iron-rich smectite (nontronite) within the metalliferons sediments was found. This pathway of clay mineral formation was shown to occur at temperatures 

1-3 years under low-temperature conditions (Michalopoulos and Aller 1995) implying significant elemental transfer into solid phase within the estuarine mixing zone. 

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