A Study On Assemblages Characteristic Of Layered Silicate Minerals In Purple Mudstone Based On XRD

The species and the relative content of the layered silicate minerals of purplish parent rocks largely determine the relative content and species that of the soil, while the species and the relative content of the layered silicate minerals directly affect the ion exchange capacity of the soil as well as its mechanical composition and fertility. Therefore, the study of layered silicate mineral combination of characteristics and relative content in purple parent rocks of different geological periods in Chongqing never fail to be important.This study was based on A Study on Layered Silicate Minerals in Purple Strata and So i I Based on XRD (Cheng Yongyi,2012), took standard layered silicate minerals and purple parents as materials, adopted methods of systematic sampling, heat treatment and comparing with standard XRD patterns. After the XRD analysis on purple parent rocks for test, a conclusion could be drawn as below:(1) Through heat treatment, the XRD patterns of standard layered silicate minerals changed as follows. The interplaner spacing of vermiculite (14.6A) and montmorillonite (15.5A) obviously reduced through320℃treatment, the diffraction peaks moved right; the diffraction peak of kaolinite (7.14A) disappeared through550℃treatment; the diffraction peak of chlorite (14.2A～14.3A)) disappeared through550℃treatment; because of high stability, the diffraction peaks of muscovite (10.0A、5.00A) and illite (4.48A～4.50A) had little change through800℃treatment, they could be identified from the X-ray diffraction patterns directly based on interplaner spacing.(2) Using the identification conditions of standard layered silicate minerals through heat treatment, vermiculite、chlorite、muscovite、kaolinite and illite in the purplish parent rocks for test could be identified accurately through320℃and550℃heat treatment. The research results were as follows.①Layered silicate minerals in Jurassic Ziliujing group purple mudstones consist of vermiculite、chlorite、muscovite、kaolinite and illite, layered silicate minerals in Jurassic Shaxi Temple group purple mudstones consist of vermiculite、muscovite、kaolinite and illite, layered silicate minerals in Jurassic Suining group purple mudstones consist of vermiculite、chlorite、 muscovite、kaolinite and illite, layered silicate minerals in Jurassic Penglai Town group purple mudstones consist of vermiculite、chlorite、muscovite、kaolinite and illite. The components of layered silicate minerals in two Triassic Feixianguan group purple parent rocks were different, layered silicate minerals in sample Tlf-1consist of vermiculite、chlorite、muscovite、kaolinite and illite, layered silicate minerals in sample Tlf-2consist of vermiculite、muscovite、kaolinite and illite.②Deriving from the regulation of mineral assemblages, we concluded that under the condition of different Jurassic geological period, even if distributed in different geographical districts and counties, the assemblages characteristic of the layered silicate minerals was almostly the same, the difference was not significant, which also indicated that the formation conditions of the purple parent rocks of the same geological period was similar. Yet Triassic Feixianguan group shows some differences. In general, the purple parent rocks for test contained vermiculite, mica, kaolinite and illite, but montmorillonite was not identified. Also, the appearance and disappearance of chlorite had no obvious rules, it might be related to the environmental conditions of mineral formation and weathering conditions, and a further study was needed.(3)The result of calculating the content of main minerals in the purplish parent rocks for test showed that the content of vermiculite or vermiculite/chlorite mixture ranged from4.5%to9.0%, the content of muscovite ranged from7.8%to31.5%, the content of kaolinite ranged from6.3%to16.1%, the content of illite ranged from8.8%to14.9%. To layered silicate minerals, muscovite owned the highest content and vermiculite or vermiculite/chlorite mixture owned the lowest content in Jurassic purple parent rocks.(4) The average content of feldspar in purple parent rocks of different geologic times showed the trend of decrease as the geologic time went on, decreased from29.5%(Triassic Feixianguan group purple parent rocks) to11.1%(Jurassic Penglai Town group purple parent rocks), and the variation coefficient reached41.6%. As the accumulation and inheritance of layered silicate minerals continued, and the total average content of layered silicate minerals in purple parent rocks of different geologic times showed the trend of increase, increased from38.6%(Triassic Feixianguan group purple parent rocks) to58.4%(Jurassic Penglai Town group purple parent rocks). But the average content of different layered silicate minerals of different geologic times showed different variation trend, from Triassic Feixianguan group to Jurassic Shaxi Temple group, then to Jurassic Penglai Town group, the average content of muscovite increased initially and decreased afterwards, but the average content of kaolinite and illite decreased initially and increased afterwards.(5)The results of crystallinity research of the main layered silicate minerals in purplish rocks for test showed that the descend order of crystallinity of vermiculite or vermiculite/chlorite mixture and muscovite was Jurassic Shaxi Temple group, Jurassic Suining group, Jurassic Penglai Town group, Jurassic Ziliujing group, Triassic Feixianguan group; the descend order of crystallinity of kaolinite was Jurassic Suining group, Triassic Feixianguan group, Jurassic Penglai Town group, Jurassic Ziliujing group, Jurassic Shaxi Temple group; the descend order of crystallinity of illite was Jurassic Suining group, Jurassic Shaxi Temple group, Jurassic Ziliujing group, Jurassic Penglai Town group, Triassic Feixianguan group.