Sedimentary Glauconites pelletal

One of the few clay minerals to be identified as definitely having an origin at the sediment-water interface is glauconite, i.e., the green micaceous material which forms pellet-like agglomerates. This has been conclusively demonstrated in recent sediments (Porrenga, 1967b Lamboy, 

In each of their occurrences in present day sediments, they become evident at a constant bathymetric level indicating the necessity of either specific temperatures or possibly pressures which, in combination with the chemistry of the sea water, organic material and the silicate sediments available permit the development of this mineral. 

The formation of sedimentary glauconite is rather similar in mode to that of chamosite or berthi rine except in the greater range of depth, 

Eh and pH at which the process takes place. In both cases the role of organic material is evident and similar, acting as a motor in changing the aspect of the silicate in the pellet both in chemistry and mineralogy from that of the enclosing sediment. The reasons for the development of one mineral species or the other are at the moment somewhat obscure but, considering the similarity of the occurrence, the mechanism is probably the same. With this in mind the analysis which follows for sedimentary glauconites can be considered applicable for sedimentary 7 X chlorite pellets. 

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Thermodynamic Description of the Formation of Sedimentary Glauconite Pellets. 

It is only implied that the process of formation of sedimentary glauconites and 7 X chlorites in pelletal form is restricted to areas near the sediment-water interface. Given the proper chemical conditions, these minerals will form at depth. These conditions, however, are probably unusual. 

Glauconites are generally considered to form as a result of the partial reduction of iron in the sedimentary materials of pellets dropped to the bottom of the sea (Hower, 1961 Thompson and Hower, 1975) although a certain portion of iron in glauconites is in the divalent state, there is neither a clear relationship between the abundance of the two valences in glauconites nor is there an evolution toward the glauconite mica end-member (Figure 2). 

Formation of nontronite from pelletal freshwater sedimentary material recalls the formation of berthierine or glauconite, but in a freshwater context (Pedro et al., 1978). Again there seems to be little tendency to form a mixed layer mineral. 

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