Chalcedony occurrences

The forms of SiC found in sediments and sedimentary rocks are quite varied but those which could be suspected of near surface origin are generally as follows quartz, chalcedony, opal, amorphous gels and ionic forms in solution. Natural occurrences indicate that the solid forms of silica precipitate which has crystallized after the time of initial deposition (Siever, 1962). 

Figure 7-B shows calculated result at 250 °C, with, Na-montmorillonite and chalcedony precipitating at an early stage (compared to the low temperature condition). Clinoptilolite precipitated at a late stage. The results are consistent with secondary minerals occurrence in the experimental system.

There are many similarities in the occurrence of biosilicification in both systems. One of the major neurochemical features of Alzheimer s disease is the marked reduction of nicotinic acetylcholine receptor in relevant diseased brain regions such as the cerebral cortex and hippocampus (Oddo LaFerle, 2006). An important use of chalcedony crystals from electric organs is, maybe, in relation with the human medicine. 

Getze, J., Nasdala, L, Kleeberg, R., and Wenzel, M. (1998) Occurrence and distribution of moganite in agate/ chalcedony a combined micro-Raman, Rietveld, and cathodoluminescence study. Contrih. Mineral. Petrol, 133, 95-105. 

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