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TEM和XRD研究表明,在苏皖坡缕石粘土矿床的蛋白石坡缕石层中存在opal A和opal CT两种结构的蛋白石。蛋白石坡缕石层主要含坡缕石、opal A、opal CT,以及少量白云石和其它矿物,由富opal A层和富opal CT层互层组成,交互层的厚度在几个厘米左右。蛋白石坡缕石层中的矿物基本是自生矿物,从蒸发湖水中化学沉淀形成。矿物组成特征研究表明,蛋白石坡缕石层的矿物组分(Si、Mg、Al)来源于盆地周围玄武岩淋滤的浅层地下水。根据Opal A和Opal CT溶解度图解和坡缕石、白云石形成物理化学条件图解,当湖水具有高浓度溶解SiO2和Mg2+时,有利于opal A和坡缕石形成,当湖水具有低浓度溶解SiO2时,有利于opal CT结晶。因此,沉淀SiO2的结构状态取决于地下水补给的湖水溶解SiO2浓度。富opal A和富opal CT交互层的形成是古气候、古水文周期性变化的指示。富opal CT层指示高地下水补给流入量,低蒸发量,湖水低盐度和溶解组分,代表湿润气候时期;而富opal A层代表低地下水补给流入量,高蒸发量,高溶解组分浓度,代表干旱气候时期。
TEM and XRD studies show that opal A and opal CT opal exist in the palygorskite layer of the Su-palygorskite clay deposit. The opal palygorskite layer contains predominantly palygorskite, opal A, opal CT, and a small amount of dolomite and other minerals consisting of interbedded layers of opal A-rich layers and opal-CT layers with thicknesses of a few centimeters. The minerals in the opal palygorskite layer are essentially authigenic minerals formed by chemical precipitation from evaporating lakes. Mineral composition studies show that the mineral components (Si, Mg, Al) of the palygorskite layer originate from basaltic leached shallow groundwater around the basins. According to the solubility diagrams of Opal A and Opal CT and the physicochemical conditions of palygorskite and dolomite formation, the formation of opal A and palygorskite is beneficial to the formation of lake water with high concentration of dissolved SiO2 and Mg2 +. When the lake has low concentration of dissolved SiO2 , Is conducive to opal CT crystallization. Therefore, the structure of precipitated SiO2 depends on the concentration of dissolved SiO2 in the lake. The formation of the interaction layer between rich opal A and rich opal CT is an indicator of the paleoclimatic and paleoclimatic periodic changes. The enriched opal CT layer indicates high groundwater recharge inflow, low evapotranspiration, low salinity and dissolved fraction of the lake, representing humid climate periods; whereas the opal A layer represents low groundwater recharge inflow, high evapotranspiration, high dissolved fraction concentrations , On behalf of the arid climate period.