桂西方解石脉型水晶晶体的形貌特征与成因

Morphology and Genesis of Calcite Vein Quartz Crystal in West Guangxi

产出于桂西碳酸盐岩地区的方解石脉型水晶晶体为透明度较好的柱状、尺型扁柱状习性。晶体上普遍同时发育三方双锥（s）、三方偏方面体（z）单形晶面。宝石显微镜、微分干涉显微镜（DIC）观察表明，水晶菱面体单形晶面生长花纹较为稳定，生长层较薄，台阶较宽；晶体锥顶和晶棱被圆化，菱面体单形晶面发育倒三角形溶蚀坑。水晶晶体中流体包裹体的均一温度为168．2—226．9℃，盐度（彬（NaCl））为6．16％～6．59％。水晶是在较低的温度、盐度、sj0：过饱和度且热动力环境较为稳定的弱碱性条件中形成的。

Quartz crystals of calcite vein type, from the carbonate regions in the west of Guangxi, have mainly prismatic habits or flat rhombohedral prismatic habits with better transparency. The trigonal pyramid （s） and trigonal trapezobedral （x） forms are apparently more common than usually found in same crystals. A careful observation is made by gem microscope and differential interference contrast microscope. The morphology of rhombohedras in quartz crystals is relatively stable, the growth layers are thinner and the sidesteps are wider. quartz crystals is 168.2 to 226. 9 ℃, and the salinity （w（NaCl）） is 6. 16% to 6. 59%. The thermodynamic crystallization environment of quartz crystal is in a stable alkalescent condition, under low-temperature, low-sa- linity and low-supersaturation of SiO2.