锆石形态标型特征及标型生长机制探讨

Crystal Form Typomorphic Characteristics of Zircon and Mechanism of Crystal Growth

本文在系统总结归纳不同研究者对锆石形态标型特征的研究成果基础上，重点从晶体生长、晶体化学和地球化学理论为重点探讨了锆石形态标型特征的生长机制。研究表明：锆石晶体结构中不同的面网方向，其平面内的原子组成、比例、化学键联结和键力以及面网间距和密度都是有差别的，由此决定了锆石晶体在不同的结晶介质条件下，不同面网的生长速度发生改变，生成相应的晶形。例如，尽管碱性元素并不进入锆石晶格，但它们可以影响Ｚｒ、Ｓｉ、Ｏ离子的扩散速度，但是富钾和富钠的介质对锆石晶形发育的影响是有差别的，表现为：在富钾的介质中，将导致柱面的法向生长速度较锥面快得多，而锥面中，｛１１１｝的法向生长又较｛３１１｝快，由此决定了形成以｛３１１｝锥为主的双锥状晶体；在富钠的介质中，柱面和锥面都有一定程度的发育，但前者弱于后者，而柱面中，｛１００｝的法向生长较｛１１０｝慢，由此决定了形成以｛１００｝柱和｛１１１｝锥为主的短柱锥状晶体。根据类似方法，论证了其它形态标型特征的客观性，从而揭示了标型之间的内在联系和本质，展示了花岗岩研究中锆石形态标型特征应用推广的前景。

Based on a systematic summary of research results available on typomorphic characteristics of zircon crystal form, this paper makes an approach to crystal growth mechanism of typomorphic characteristics of zircon with the help of theories of crystal growth, crystal chemistry and geochemistry. The results show that there exist differences in composition and proportions of atoms, links, power of chemical bonds, intervals and densities of crystal lattice faces in different directions of its crystal structure. These differences affect growth velocity of crystal lattice faces in different directions and control corresponding crystal forms under different conditions of crystalline media. For example, alkaline elements can affect diffusion velocity of Zr, Si and O ions although these alkaline elements cannot exist in crystal structure of zircon. However, K rich media and Na rich media exert different effects on the growth of crystal form: in the K rich media, growth speed of prism faces in the vertical direction is much higher than that of pyramid faces, and {111} growth speed in the vertical direction is higher than {311},which decides the formation of bipyramids dominated by {311} pyramids; in the Na rich media, both prism and pyramid grow to a certain extent, but the former is smaller than the latter. {100} growth speed in the vertical direction is lower than {110}, while {111} growth velocity in the vertical diredtion is lower than that of {311},resulting in the growth of the crystal form characterized by {100} short prism and {111} pyramid. With similar research method, this paper has proved the objective nature of the typomorphic characteristics of zircon, brought to light the internal and innate relations among typomorphic characteristics of zircon, and opened up the prospects of applying these characteristics to granite study, thus providing more analytical and applying value to single zircon grain geochronometry.