The Mineralogical Study Of Agates In The Sedimentary Gravel Layers From Fangshan, Luhe County, Nanjing

FT-IR data indicated the dominant mineral was a-quartz, in addition a little bit water molecule was included;In situ Laser Raman detection showed that there extisted no difference between chalcedony and quartz with their vibrational spectrum. We found a lately discovered microstalline silica mineral moganite within the wall-ling bands.which was characterized by the Raman peak at505cm-1. By comparing the spectrum of different sites,we discovered the uneven distribution of moganite,which was ususally mixed up with chalcedony rather than fine quartz, thus its formation conditons were more strict.Agates under the polarizing microscope mainly showed granular, fibrous. Bunched fibers were generally parallel to each other or intesected at a small angle. The orientation of fibers was perpendicular to the bands, and there existed rhythmic extinction. The colored bands could either be made up of fine-quartz or chalcedony, and crystal size of the latter was smaller than that of the transprarent layers. We proposed that agate growed up from its outer rim to the center.Scanning electron microscope showed tiny globulites and sheet structures, but no fibres; in addition, we found the plate-edge like stucture. The abundant pores and several curly films suggested evaporation The water vapor evaporation. BSE images showed no band and the uniform brightness, so there existed little difference in its compositon. EDS detected some elements, including Cu,Fe,Na,K,Ca,S,Cl,Al,Fe,and so on,which indicated that the agate initially formed in some fluid.Under atomic force microscope a morphology similar to quartet cone with its straight edge analogous to parallel fibres had been observed, which might stand for moganite. Its surface height showed higher on the left part than the right, and displayed a tendency that fibers came from spheroids.Although the agates of this study were found in sedimentary environment, they were not a simple siliciclastic consolidation,but might form in a solution, which was rich in crystalline and partially polymerized silica. The fomation of bands might be related to a analogous self-organizaion preocess. Agates formed in an oscillatory environment, thus, the process was very complicated and controlled by several factors. The mineralogical study of agates filled the domestic blank in the research of agates, and introduced a new silica polymorphism moganite, meanwhile might contribute to the production, fabrication processing and comprehensive utilization of nanoscale silicon material.