四川平武富碱型绿柱石晶体的晶格缺陷与生长机制

CRYSTAL DEFECT AND GROWTH MECHANISM OF ALKALI RICH BERYL CRYSTAL FROM PINGWU,SICHUAN,CHIAN

在低饱和度、碱性、气成—热液条件下形成的四川平武绿柱石宝石晶体 ,具有特征的扁平板状几何外形。在绿柱石晶体的 { 0 0 0 1}、{ 10 10 }、{ 112 1}面上 ,普遍发育螺旋位错、束合螺旋位错、层错及接触双晶 ,它们共同构成了绿柱石晶体生长的主要台阶源。微分干涉显微镜、扫描电镜和透射电镜研究结果证实 ,由填隙变形、位错滑移和水解弱化等综合作用 ,直接导致绿柱石硅氧四面体六方环结构和铍氧四面体结构的局部畸变 ,并相应引起多面体体积、化学键力、键合能及晶面的法向生长速率发生变化 ,从而决定了该区绿柱石晶体生长的形态。由绿柱石晶体中的线缺陷 (螺旋位错 )、面缺陷 (层错、双晶 )及点缺陷 (空位、包裹体 )的协同作用 。

The beryl crystal from Pingwu County, Sichuan Province that occurred on the low-saturation, alkaline and pneumatogenic - thermal conditions, is characterized by the flat tabular shape. On the crystal surfaces of the beryl crystal at {0001}, {101 over-bar 0}, {11 over-bar 21} occur universally screw dislocation, constriction screw dislocation, stacking fault, and contact twin that serve as the major step-like source for the growth of beryl crystal. The research results obtained through differential interference microscope, scanning electron microscope, and transmission electron microscope show that the comprehensive effects of interstitial deformation, dislocation sliding and hydrolytic weakening lead directly to the local deformation of the silica tetrahedral hexagonal ring-like structure and the beryllium oxide tetragonal structure, and at the same time to the change in polyhedral volume, chemical bond force, bonding energy, and in the normal growth rate of the crystal face. These changes determine the morphology of the beryl crystal growth in this zone. The formation of the flat tabular beryl crystal in Sichuan Province is attributed mainly to the synergy of the linear defects (screw dislocation), face defects (stacking fault and twining) and point defects (vacancy and inclusion) in the beryl crystal.