Celadonite origin

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. 

Since this review was originally completed, Foster (1969) published a review in which similar conclusions are drawn about the glauconites and celadonites. The lack of correlation between iron and potassium content in glauconite is substantiated in her paper. Foster considered the process of glauconitization to be of two separate, unrelated processes, incorporation of iron into the crystal structure and fixation of potassium in interlayer positions, with incorporation of iron and development of negative layer charge preceding complete fixation of potassium . 

The Fe2+ content of celadonites (continental origin) and glauconites (marine origin) is identical suggesting that its abundance is not controlled by environmental conditions. Structural control is more likely. Apparently, layer strain is less and the structure more stable when there are 0.20 large Fe2+ ions in the octahedral sheet. 

The formula Dim is that of an idealized Al-celadonite, Bio is that of an idealized phlogopite, and Chi is that of an idealized clinochlore. (Dim + tk) is, of course, the idealized muscovite formula (Bio + tk) is that of an idealized eastonite, and (Chi + tk) is that of an idealized corundophyllite. The last two are taken as the extreme tk+ limits on the basis of the aluminum avoidance rule. The choice of the clinochlore formula as the tk- limit makes good crystallo-chemical sense for 14-Aigstrdn chlorites, the ones found in pelitic schists. The original chlorite structure described by Pauling (1930) was, in fact, that of a clinochlore found in a blackwall skarn in close proximity to a lizardite-bearing serpentinite near Chester, Vermont, U.S.A. The idealized lizardite formula may be taken... 

Intergranular zones occupied by glassy material are frequently observed (Fig. 6). This process produces abundant clay minerals. Montmorillon-ite, chlorite and a small amount of celadonite were determined by XRD. In other sectors isotrope material, (considered relictic from the original pal-agonite) was observed. Apatite is abundant. 

Odin Delamare (1986) Odin, G-S. Delamare, R Nature et origine des phylUtes vertes utUisees comme pigment dans les peintures murales romaines en Gaule celadonite et glauconie C. R.Acad. Sci. 302 11 (1986) 745... 

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