Glauconite sedimentary

Glauconite Sedimentary rocks, low hydrothermal in igneous rocks ( ) a) From illite syn-sedimentary or by diagenesis (dissolution-repredpitation) b) From colloidal solutions in pore spaces of marine sediments To illite by leaching Neoformation in sediments or synsedimentary... 

The Nishikurosawa Formation is composed of siltstone, mudstone, conglomerate and sandstone. Siltstone and mudstone contain foraminiferal fossil such as Globorotalia birnageae, and G. denseconnexa, indicating Zone N. 9 by Blow (1969). The upper part is characterized by glauconite-bearing sedimentary rock. The total thickness is about 150 m. 

It is interesting to note that the 1M polymorph represents an ordered form while lMd structures are disordered (Guven and Burnham, 1967) and that the typical sequence in the process of glauconitization is lMd to 1M (Burst, 1958). Illite remains, for the most part, disordered even in Paleozoic sedimentary rocks (Velde and Hower, 1963). This would suggest that the glauconite structure, being more symmetric, might be more stable than illite, a point which will be discussed when experimental studies are considered. 

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. 

Thermodynamic Description of the Formation of Sedimentary Glauconite Pellets. 

It is obvious then that A1 is not synonymous with Fe in sedimentary mica-like minerals. The increasing influence of trivalent iron in a sedimentary system will obviously provoke the crystallization of a specific mineral series which is not contiguous with illite and which would not be present otherwise. The development of glauconite in sediments should be due to specific local conditions which permit the chemical evolution of an initial montmorillonite material to celadonite mica-like phase. In fact previous observations have consistently led to this conclusion as to the origin of glauconite in sediments and sedimentary rocks. 

In addition to proper biotic factors, it appears that the oxidation state of the iron in the sediment is critical to the formation of sedimentary 7 8 chlorites these conditions are more reducing than those which form glauconites (Porrenga, 1967b Leclaire, 1968). As is the case for... 

Two phase assemblages of any of these minerals are known. It should be noted that aluminous phases, such as kaolinite, have never been reported with corrensite neither are sedimentary phyllosilicates such as 7 8 chlorite or glauconite. Non-phyllosilicates in association with corrensite frequently include diagenetic quartz, albite and dolomite. Pelitic rocks, specially associated with those containing corrensite, contain allevardite and fully expanding montmorillonite (dioctahedral). 

Most commonly, zeolites are found in series of sedimentary rocks which contain pyroclastic material and are formed during the devitrification of this material. If the rocks are silica-rich, the zeolite species formed seems dependent upon the bulk composition and burial depth or temperature of formation (Hay, 1966). They are most frequently accompanied by silica in an amorphous or cryptocrystalline form (opal, chalcedony). Analcite and all other compositional intermediates up to the silica-rich clinoptilolite are found in this association. The most comifton clay mineral in such tuffs is montmorillonite. Zeolites are sometimes found with glauconite (Brown, et al . 1969) or celadonite (Hay, 1966 Iijima, 1970 Read and Eisenbacher, 1974) in pelitic layers or acidic eruptive rocks... 

Two minerals frequently encountered in sediments and sedimentary rocks are not accounted for in the Figures 48a to c. These are glauconite and chlorite, the two major iron-bearing phyllosilicates in sediments and sedimentary rocks. Glauconite formation can be explained on the basis of... 

The initial increase in hydrostatic pressure in a sedimentary basin appears not to change mineral stabilities from those of the weathering environment. The formation of potassic, iron-rich micas such as ferric illite and glauconite both in lacustrine and shallow ocean basins demonstrates their stability at low pressures and temperatures. The same is true of the 7 8 chlorite chamosite or berthierine. Most likely the chemical variables of pH, Eh and the activity of the various ions in solution are predominant in silicate phase equilibria in sedimentary environments. 

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. 

Glauconite, being of sedimentary origin, can he used to determine the age of those sediments by evaluating its Ar ratio (potassium-argon isotope ratio). See also Ocean Resources (Mineral). 

Evernden, J.F., Curtis, G.H., Obradovich, J. and Kistler, R., 1961. On the evaluation of glauconite and illite for dating sedimentary rocks by the potassium-argon method. Geochim. Cosmochim. Acta, 23 78-99. 

Chemical conditions. The occurrence of glauconites in sandstones (acid) and carbonates (basic) indicates that pH is not of great importance to their formation. They are found in sedimentary rocks ranging in age from Precambrian to the present day. Hence, their formation seems to be constrained by chemical and physical conditions rather than by specific events. There is no apparent time-dependent reaction which transforms them into new phases. 

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. 

Chang C-M, Wang M-K, Pan Y-C, Tseng P-K, Chen P-Y (1993) Refinement of nontronite, celadonite and sepiolite Mossbauer spectra at 77 K temperature. J Geol Soc China 36 189-202 Chen R (1985) Study of the mineralogical characteristics and sedimentary environment of glauconite from some regions in China. Petrol Res 5 91-101... 

Bentor, Y. K. Kastner, M. 1965. Notes on the mineralogy and origin of glauconite. Journal of Sedimentary Petrology, 35(1), 155-166. 

Hydromicas are authigenic minerals rather easily forming in a sedimentary environment. Fe-illites would be the analogs of glauconites in gradually salting-up basins. The out-flow of bottom waters and the fixation of the bivalent cations Ca and Mg " (in dolomite) in case of a relatively low concentration of the latter (sodic-calcic lakes) lead to the relative enrichment of these in potassium. The latter will then be fixed by the silicate compounds in solution leading to the synthesis of Fe-illites. In case... 

The final step in the interpretation process is to derive mineralogy from the specific lithology. A list containing some of the common sedimentary minerals used for formation evaluation is provided in Table 5.18. Potentially identifiable minerals are quartz, potassium-feldspar, albite, calcite, dolomite, siderite, anhydrite, iUite/smectite, kaoUnite, glauconite, chlorite, pyrite and others. 

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