两种不同燧石中α-石英 β-石英相变的研究

A STUDY ON α-QUARTZ β-QUARTZ PHASE TRANSITION OF TWO KINDS OF CHERTS

利用差热分析和高温 X-射线衍射分析的实验手段,对两种不同燧石的α-石英β-石英的相变反应进行了研究。结果表明,它们在相变热效应和晶格参数随温度的变化规律等方面存在着明显的差异。这种差异性的存在是由于两者内部α-石英颗粒的粒度、双晶发育程度以及燧石本身的致密度不同所造成。

The transition of α-quartz β-quartz of two kinds of cherts,which are taken from the Carboniferous carbonate rock at Hongshuihe,Guangxi,Region,and the Permian carbonare rock at Jiangnan,Jiangsu Province,respectively,and standard quartz were studied by DTA and high-temperature XRD analyses.The resul,of DTA indicates that the DTA curve of Hongshuihe chert is very similar to that of standard quartz,but the DTA curve of Jingnan chert is distinct from those,i.e.there is no valley of transition heat effect at 573℃ on it.The result of high-temperature XRD analysis indicaes,that the α-quartz β-quartz transition on three samples occurs at 537℃,and the whole process is continuous.The lattice parameters of α-quartz in three samples are approximately equal at 25℃,but when β-quartz is formed,only the lattice parameters of β-quartz from Hongshuihe chert and standard quartz are very similar, and those from Jiangnan chert is smaller than the stantard,The difference between jiangnan and Hongshuihe cherts described above are due to their different characteristics.The result obtained by electron microscope indicates that the grain size of Jiangnan chert (about 0.2— 0.4μm) is smaller than that of Hongshuihe chert (about 10μm).but its compactibility and number of twins are larger.As it is known,the transition heat declines with the reduction of grain size of α-quartz,and the single crystal size of α-quartz from Jiangnan chert is very small,hence it exhibits a negligible heat effect.For the same reason,as the powder of Jiang- nan chert,which is used in high-temperature XRD analysis,is the assemblage of α-quartz cry- stals,and its compactibility is very high,thus the transition of single crystal of α-quartz_3 which is limited by the adjacent crystals,is commensurated with the transition of pressed cry- stal,and the lattice parameter of β-quartz is smaller than that of Hongshuihe chert or standard quartz.