摘要
一、引言 戈斯(Ghose,S.)在测定斜方辉石的结构时,首次发现Fe^(2+)离子择优占据M^(2)晶位,而Mg^(2+)离子择优占据M1晶位。这一事实,引起了矿物学家的极大注意。自本世纪四十年代开始,人们已经注意到Fe^(2+)和Mg^(2+)离子在硅酸盐矿物的共生对之间(例如橄榄石和斜方辉石,斜方辉石和单斜辉石等)的分配规律,并使用热力学理论加以解释,试图阐明地质体的平衡温度和压力,这一类研究归结为Fe^(2+)-Mg^(2+)阳离子的晶间分布(intercrystalline distribution)。
Extensive study has been made on orthopyroxenes by X-ray diffraction and Mossbauer resonance technique,and the intracrystalline distribution of Fe^(2+)-Mg^(2+)over M1 and M2 sites has been determined.Fe^(2+)ion is strongly preferred at M2 site while Mg^(2+)at Ml site.Several workers have interpreted the orderly-disorderly kinetics in terms of ideal solution model and simple composite model.In this paper site distribution data are used to calculate the Fe^(2+)ion energy difference between Ml and M2 sites,by assuming Boltzmann distribution of ions over the sites and the blacking of sites as a result of preferential substitution.From the results calculated it is inferred that there are composition-dependence and temperature-dependence for Fe^(2+)ion energy difference △E_(12) between Ml and M2 sites in ortho-pyroxene.According to classical thermodynamics and kinetics Virgo and Hafne have given the value of activation energy E_(0)=16.5 Kcal/mole for orderly process and E_(D)=20 kcal/mole for disorderly reaction,thereof △E=E_(D)-E_(0)=3.5 kcal/mole is in good agreement with our results.The value △E_(12) obtained in this work can also be used to interpret the influence of annealing temperature and compositional changes on relative site distribution.
出处
《地质科学》
1979年第2期151-156,共6页
Chinese Journal of Geology(Scientia Geologica Sinica)
